I assume by “trick” you mean having a second, knotted stem hidden in your cheek.
Ask a sucker to fold up a bill (the greater value, the better) and place it under a coffee cup. Tell him that you’ll bet him your own money against his (under the cup) that you can take the money without touching the cup. Make up a spiel and then tell him you have the money. (You might show a duplicate amount you pull from your pocket.) If he doesn’t believe you, tell him to look for himself. When he picks up the cup, you take the money… without touching the cup!
I’m rather sure that my esteemed colleague Hastur does NOT mean that at all. I too can tie a cherry stem into a knot in my mouth.
There was one evening when I had to tie many of them into knots very rapidly, one after the other. Apparently a troup of girl scouts had fallen over a ravine, and if not for my linguistic contortions, there would have been NO cherry stem rope with which to haul them to safety. 
It’s not that hard to do, really. Want me to teach you how? 
Cartooniverse is quite correct. I can tie a cherry stem into a knot with my tongue, which I have demonstrated many times in bars. I’ve also done it with a bar straw(takes a little bit more time).
Well Hastur, as this thread is entitled “Bar tricks anyone can do” I guess you’re just going to have to teach us all… 
You need a very flexible tongue, and you have to be able to visualize as you do it so you have an idea that you are knotting it. It generally comes out like a pretzel.
My favorite is one that requires no special equipment–just an empty beer bottle and a room with walls that are painted (as opposed to brick, concrete, wallpaper, etc.). I think it has to be latex paint; either that or it can’t be latex paint. I forget which, but when it works, it’s really cool.
All you have to do is rub the bottle up and down on the wall where there is a corner (where two painted walls meet). If you rub it right and let it go gently, it will simply stick to the wall, suspended in mid-air for a good long time (a few hours was our record). The paint heats up just enough to make it sticky and suspend the bottle.
Try it out if you don’t believe me; just be careful, as sometimes the bottle will leave marks on the wall and/or drop suddenly just seconds after you get it to stick. It does amaze people when it works, though. Also, be sure to practice it beforehand to be sure the room has the suitable type of paint.
Cheers!
I do a lot of Rubber-Band magic and this one fits the subject perfectly:
Props:
A bunch of #19 rubber bands
Setup:
Start by taking one rubber band and rolling it up. Place it in your mouth between your cheek and gum. Take about 5 to 10 rubber bands and place them around your right wrist.
Performance:
Take one of the rubber bands on your wrist and while keeping it on your wrist, streach it out between the thumb and forefingers of both hands. When done properly, it will look like a streached out rubber band between your hands. No one will suspect that it is also looped around your wrist.
Hold the left end of the “streached” rubber band up to your nostril and hold your right hand down from that so that the rubber band is at an angle to your nose, then let go with both hands at the same time. The rubber band will snap back to your wrist, but look like it went up your nose. If you add a “sniffing” sound to it and a little head action, it really looks like it went up your nose. I always embellish the performance by pretending that it really hurt. It gets a huge laugh. Meanwhile the rubber band you snapped returns to your wrist along with the others there and no one even knows it has returned there.
At this point, I motion for people to wait. I make a few facial movements that make it look like I’m snorting it through my sinuses and at the same time, work the rubber bank in my mouth to my front teeth. Then I slowly remove the rubber band from my mouth and hand it to someone saying, “Here, you want to try it?”. I always get a laugh and a very hasty “No!”.
Sick stuff, but hey, I’m a magician. We’re all sick.
A lot of the old fashioned pubs in Australia have tiled walls. Apparently this trick works on the tiles too, though I’ve never seen it done. The version I heard was that instead of a bottle, you use somebody’s half full beer glass while they’re in the bathroom. When they come back and ask where their beer is, you point halfway up the wall.
- Make sure all of your victims have a sense of humor.
- Ask if they’ve ever seen a hair fight.
- Get a plate and a glass of water.
- Pluck a hair from each of the victims and put it in the plate. Add one of your own as well.
- Tell everyone to watch REALLY CLOSE and keep track of their own hair.
- Pour the glass of water into the plate with the hairs.
- Watch intently for a couple of seconds; make sure everyone else is doing the same.
- Very quickly slap your hand in the plate as hard as you can, splashing the hell out of everyone.
- Claim that your hair won.
Equipment: a drink, nine coins, a coaster or napkin, and an accomplice, along with several other people unaware.
Set up: You have extremely sensitive fingertips that can sense tiny heat differentials. Arrange the nine coins in a three by three matrix, and ask one person to touch one coin while you are out of the room. Leave the room. Come back, place your hand hovering just above the coins, wandering from one to the next, (add theatrics to taste) and choose the one touched.
The trick: Your accomplice places his or her glass/bottle/can on their coaster/napkin, which is aligned with the matrix, in one of nine positions on the coaster
X X X
X X X
X X X
if this coin touched, accomplice places glass in the the upper right of their coaster. If two coins or no coins are touched, keep glass in hand and do not put it down. Your reaction is fingertips do not give good info, and you can say “It doesn’t work ALL the time”, or “maybe my fingers got too cold”, but don’t blame anyone for cheating.
Works again and again.
Damnit, Lowellster, you just listed my favorite one! Except I just pour a little puddle of water directly on the bar or table. I give some story about how the different static electricity in people’s hair will make it appear as if their hairs are fighting. I love it. A couple more of my favorite bar jokes are…
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Show people my broken nose. Tell people that you’ve broken your nose, or that the cartilage in your nose is messed up. Put your hands flat together, palm to palm like you’re praying and hold on to your nose. Your thumbnail should fit right next to (behind) your front teeth. Turn your hands from one side to the other like you’re bending your nose to the side. As you do this, ‘click’ your thumbnail off your front tooth. Guaranteed to give people the heebee jeebees.
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Show people what Dog Jaw is. Another fave to get a reaction from people. Only one possible victim with this one. Steer the conversation where you mention ‘Dog Jaw’. When someone asks what Dog Jaw is, ask incredulously: “You’ve never heard of Dog Jaw? Here, Feel this…” as you point to the side of your face where your jaw ends. As they innocently reach their hand up to touch your jaw, in once quick motion… jerk your head towards their finger, do a dog snarl/growl, and snap at their finger. Guaranteed to make them scream.
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Play a game of Quarter Basketball. Bet a friend that you can beat him Quarter Basketball. The Rules are simple. Draw a starting circle around a quarter on a piece of paper, and roll the quarter off your face. Whereever it hits the paper, draw another circle the size of the quarter. Do this 10 times. Count the circles that are touching another circle. That is how many points you get. Either person can go first, but make sure you’re the one drawing the circles. Here’s the trick, with a pencil, draw a really dark circle around a quarter, making sure to get graphite on the edges of the quarter. Each time he drops the quarter down his face, he’ll be leaving a trail down his face that he won’t know about. It’s funny as hell.
I’m sure there are other variations of this last one. One involved getting the person to roll the quarter all around their face.
Enright3
I can vouch for that broken nose thing. Except, I don’t need to fake it.