I guess this counts even though it was at a party, but I kinda beat up an audience member.
We were third to play a huge out of control BBQ/house party. I don't know how we ended up there, I loved party gigs but it was not our kind of crowd, all drunken frat boys. We played punky blusey stuff, think Mudhoney meets Kyuss. It was a super hot humid day with fights breaking out and the first two bands were terrible. Stopping several songs cause they kept getting lost, 15 minute out of tune renditions of the Beastie Boys "Fight for Your Right", AC/DC covers that somehow had only one riff and no chorus, really bad stuff. We'd been doin our thing for a few years with a small following and had 45 originals, which all this is to say most of us weren't into this party anymore before we even started playing.
We start playing and its going well enough...then I got pelted with raw ground beef. I saw the dude rear back with another handful, I took off my bass and dropped it face first against the cab, walked down the steps into the crowd and got in his face. Words were briefly exchanged, there was some shoving, and...I lost it. I kicked him in the nuts and double fist sledgehammered in the back, asked if any one else wants to throw stuff and stomped back up the stairs. To their credit the band never missed a beat even with my amp squealing feedback. I got back on stage, shut off my rig and waited for the song to end. I told them what happened and my brother (the drummer) got on the mic and I cant repeat what he said according to forum rules governing cursing. That was the last song of the night, we just started packing up with or without the rest of the band. We did 25 minutes out of 2+ hours.
I'm not proud, its kinda embarrassing in hindsight, but I'm not completely ashamed. I never would've done that at a club gig, but this was different. Granted 4 out of the 6 of us in the band were kinda wimpy stoner nerds and looked like easy targets, but my brother and I, however, were not. We grew up cutting our teeth in the pits of the thrash metal and hardcore/skinhead scenes for years in Boston and Providence, so when some dumb kid from the 'burbs pelted me, my bass, and my speakers with raw ground beef...well... Honestly, they're lucky they didn't get my brother with the raw meat, he's the one with the temper and was rockin his newly acquired '77 rosewood Sonor kit that night, the dude woulda ended up with something broken.