Found an old thread on it here (semi-tangentially related). Wiki article. Something I’ve always wanted to do, but of course as the linked thread demonstrates it could be taken a bit too far.
I played something like that once, when I was in college. It was so long ago that I don’t remember whether it was fun or not.
Played throught my freshman year of college. It was pretty cool.
I won the first game we ran by tagging a guy with a stick of Chapstick. The GM then ruled lethal contact poisons couldn’t be applied directly to a person. That led to me dying in the next game via Vaseline on my car door handle. That saved me from being victimized by the bomb left on a friend’s computer (planted via the word “BOOM!” left on a sticky note).
The last game we ran was warring teams with “budgets.” The very first day, the opposing team blew their whole budget on a bomb that blew up the entire dorm. I survived because I didn’t live there.
The entire time I carried around a Nerf gun, but never got a chance to use it (we couldn’t have witnesses).
I organized two Assassins games in the dorm back in college. In my version, you had to kill your target by tagging him/her with a sock. They were big games, with 50-75 people involved in each. Lots of fun.
When I set up the first game, it was just a few months after 9/11. There were lots of dorm-wide e-mails with subject lines like “WHO’S INTERESTED IN A GAME OF ASSASSINS?” One of the RAs (the upperclassmen who lived in the dorm to enforce university rules) approached me and asked me to change the name of the game. In light of “the terrorists and everything.” I asked if there was any other problem with the activity other than the name. She said no, it was just the name that was a problem. I told her I wasn’t changing the name. She was dumbstruck – it hadn’t occurred to her that I might refuse. You could see in her eyes visions of self-righteous college freshmen protesting for Free Speech. She mumbled something, dropped the subject, and fled.
I organized it for our high school in the late 70s. It was a blast. Don’t think it would work nowadays; some kid would get shot by an overzealous cop.
ETA: we played the with those old fashioned little rubber tipped darts. Our biggest game had 120 players. We called it T.A.G. (The Assassin Game) but also KAOS (Killer As an Organized Sport) It was almost as much fun to run the games as participate.
Spring of my sophomore year at Northwestern (1996) one of the fraternities on campus (Pi Kappa Alpha) set up a campus wide Assasins game as a philanthropic effort. You had teams of 5 characters, one of whom was the captain (though, only your team and the organizers knew who the captains were). Each team was assigned another team captain to take out. And you had a time limit of a week to do so. If you didn’t get the captain in time, you were out of the game. If you did, you would get the next captain after the end of the current round. Water guns were the weapon of choice. Cheap ones were provided as part of the registration fee, but you could use any water gun of your own if you wanted to. We managed to take out 3 of the 5 of the team we were assigned to, but didn’t get the captain. The team who was after us didn’t manage to take any of us out. And the team we were assigned to take out didn’t get their target captain either. From what I understand the vast majority of the teams failed in the first round.
Once you were shot as a target, you were out of the game permanently. However, the targets could defense shoot an attacker, which would temporarily knock the attacker out of the game for an hour, letting the target escape.
Don’t know if anyone’s every seen this, but there’s a group that do something similar called StreetWars (http://www.streetwars.net/), but you can use water devices/guns only (homemade, water balloons, etc.). $45 per person, lasts three weeks, 24/7. There is one organizer, and everyone gets dossiers on their “targets.” If you are killed, you are to turn the dossier for your target over to the person who’s killed you. And so it goes until there can be only one.
The blog and the stories can be pretty funny, and some of the assassinations are actually pretty clever. I think it’d be fun to do, but it appears they only do it in major cities.
I played a light version of it at a summer camp - the rules were that we were only allowed to try and kill our targets during meals, as it would have caused too much chaos in the general operation of the camp otherwise.
There were 4 weapons :
- the bomb, which was a bit of masking tape you had to put under the target’s chair. If he sits up without noticing it, boom
- the poison, same thing but under a plate/glass
- the radioactive particle, an Othello game piece you had to put in their pockets, if they left the room with it, dead
and finally - the Manchurian candidate, a weird phrase assigned to you. If you manage to get your target to say it, he dies. I don’t think anybody ever managed that one.
You were only allowed to kill your predetermined target, so no putting poison under the collective jar of water or bombing the whole table instead of the chair (yes, of course somebody tried 
)
The paranoia was exquisite, with everyone entering a kind of survival routine… and I must say, it’s amazing what people won’t notice. A friend of mine dropped quietly under the table mid-conversation, crawled under the whole length of it in full view of half the (giggling) room, and bombed his target who, since he had already checked for bombs before sitting down, didn’t bother checking again when he was innocently asked to go and fetch some more water. Boom.
I played that alot in college. We limited the weapons to those disk shooter toy guns and no witnesses, although you could get around that by killing the witnesses as well. We had a lot of fun, but it definately raised the paranoia level in the group (my last game death I was assassinated by my GF…on valantine’s day. Yeah, love you too honey.)