One rule: it can just be one sentence. Feel free to include the context or not.
Mine - a pissed-off woman on the payphone at the mall: “He SAID he was just taking the garbage out, but he never came back!!!”
Funny to me because it was such a cliche … maybe I am going to hell.
Okay, what are yours?
Guy working out with me at aikido: “Zen, okay, zen… What is the sound of shit happening?”
“We met when I was a tree-sitter and he was in the circus…”
1 of 3 teenage girls addressing a Romney ewe chewing hay in a corral at the last day of the fair: “You’re ugly and we hate you!”
Geez, it’s tough to be a girl in Southern California, no matter what species!
Argentina… Is that in Canada?
Overheard in my office. I am a travel agent. It may really be too sad to be funny.
Scene: In front of the TV in a Hampton Inn lobby in Minnesota last month. That Frosted Mini Wheats commercial comes on where the Mini Wheat says to the little girl in the spelling bee, “Aardvark. It’s the first word in the dictionary.”
Guy 1: Heh. The first word in the dictionary isn’t “aardvark.” It’s “a.”
Guy 2: “A”? I thought that was a letter.
Guy 1: Not “a” the letter, “a” the word. As in “take ‘a’ hike.”
“Just because she wouldn’t go on a date with me doesn’t mean I have to stop thinking about her when I masturbate.”
I work at a summer camp for kids age 5-12, many of whom are naturally overinterested in the love lives of we counselors. 
At lunch today:
Ten-Year-Old Girl: You’re dating Counselor #1, right?
Nine-Year-Old Girl: Is she your girlfriend?
Counselor #2: Uh, yes. Yes, she is.
Ten-Year-Old Girl: Have you kissed her yet?
Nine-Year-Old Girl: Have you proposed?
Counselor #2: Whoa, slow down! You’re asking about kissing and suddenly I have to propose?
Nine-Year-Old Girl: Have you hugged her?
Ten-Year-Old Girl: I’ve hugged. I’ve been hugging since the fifth grade. [deliberate pause] And I’m in the fifth grade.
Exasperated female half of a couple exiting their vehicle next to mine as I’m loading my purchases into my car in the Walmart parking lot: “No, Walmart is NOT for trashy people! This lady [gestures to me] shops at Walmart!”
Um, thanks… I think.
Saturn peaches are the peaches of the future!
Gracie Allen: “She is the man who owns the grocery store’s sister.”
Man on cell phone: I got a tatoo by myself. I got a gun by myself. I can certainly go to the movies by myself.
Would it be out of order to request this as a sig line? 
Wind my life back 25 years and this is so reminiscent
I’ve posted this a million times, but I still find it hilarious.
“Just close your eyes and try and touch someone” - a brief description of the rules to the game of Marco Polo!
A friend of mine on his neighbor: “I couldn’t hate that b!tch more if she was made of fat free mayonaisse.”
I overheard a (nursing home) resident talking to their daughter on the phone: “Well I had peaches. I think they were peaches, they felt like peaches when that crazy lady threw them on me but they didn’t really taste like peaches. Should I ask the nurse, or…oh what where you saying dear? No apricots, yes peaches…”
Not too recent, but still damned funny:
“Axl Rose? Who the hell is that fat, old queen?”
“That’s not sexy! You’re just spreading e-coli everywhere! Look, now it’s on her, now it’s on him…”