You gotta narrow it down. There's LARP like the SCA, which is basically real fighting with armor, swords and beating the crap out of people, the stuff is just blunt. The midevil flair is a bit geeky, but I think even the most jock-ish football player would have to look at people in PVC piping armor beating the living crap out of each other in massive 100 man melees, and say, "Dude, that's hardcore".
The LARP that Ive personally done is World of Darkness LARP, primarily Vampire, but other World of Darkness venues as well (Mage, Werewolf, etc). Ive been part of the Camarilla, the big, official club, before, and Ive learned a very important thing about LARP. It's like any other RPG, just with more visual aids and speaking in character, with particular appeal to people who want to game in large groups, and a bonus if you like costuming. The only problem with LARP is LARPers. In the same way Video Gamers are filled with fat, depressed losers, LARP is filled with creepy, emo-goth weirdos. It is all about who you play with, and you have some control over that. If your not with a bunch of weirdos, its actually pretty fun.
Oh, and people say that they like girls? Well, imagine a PnP RPG you like. Now imagine it's almost half girls. Girls who, naturally, are probably dressed in corsets or other revealing attire. And they spend a few hours around you, gaming, and treating you like your a fellow bad ass. You have a completely legitimate excuse to flirt with them, and often times at the end of the night you go and party. I have to admit that ive used LARPing as an excuse to regularly flirt with a smoking hot girl.
Oh, and did I mention that your male competition is other LARPers? Yeah, the only thing standing between you and hot girls in corsets is LARPers.
