Things You Don't Want To Hear Your Bandmates Say On Stage...
1. From the drummer: "How does this song start again?" SMG had a rotating roster of drummers, and we got short-shrifted once by a guy that rehearsed well, but didn't do so hot on stage. SMG songs were, for the most part, straight-ahead rock numbers. One, and only one, was in triplets. So I'm announcing the song, and I hear him behind me asking the guitarist how the song starts. I don't think much of it, but I count off, and he starts it in straight time. So I stop the song, turn around to him and say "hey, this is in trips!" I count it off again, and he starts it in straight time _again._ So we repeat the above. I count again, and he starts in straight time a third time. I turn around, grab his cymbals and go "stop, motherfucker! TRIPS! You know. 123 123!" He was fired shortly thereafter.
2. From the guitarist: "How does this song start again?" See above.
3. From anybody but the drummer: "What key is this in?" The worst is when you're already playing it, and you can tell something is wrong, but you're not sure what. All of the sudden, a solo section comes up, and it's blindingly obvious that someone is playing a half-step off. I hate that.
4. From anybody but especially the drummer: "Dude, I'm soooo fucked up!" This is a hard thing to hear about the third song in, because you know the rest of the set is gonna be a trainwreck, and there's nothing you can do about it. I've had a long-standing policy that someone that gets fucked up before a show won't be playing the next show. I can play every instrument but drums well enough to pull off a set, so I don't have any problem shitcanning someone for unprofessionalism.
5. From anybody, in the middle of a song: "What the fuck?" Or alternately, "dude, my shit is fucked up!" 99% of the time, this is from the guitarist, and is a result of a pedal malfunctioning, and usually this is because he didn't change the battery. You'd think they'd learn.
6. The worst thing of all doesn't come from on-stage, though. Rather, you're playing what you thing is a really good set, and you look up, and you see the soundman with a look of panic on his face as he stares at the console, and his arms outstretched, palms up, in the universal "what the fuck?" gesture. There are few things that can take the wind out of your sails like that.