Don't mean to sound like grumpy old guy, because I had a total blast (again), but...
1. Plowing forward with your boyfriend and your backpack into the front of a crowded set and banging said backpack on the people (i.e., me) in front of you. If you want to get up front, get there early people. If you're gonna plow through, it better be to go mosh with Social D.
2. Texting your buddies to come find you, only the texting is done with hands over-head, which is followed by holding said phone up so that said buddies could find you.
3. Swaying and dancing to good music (ok, good so far) and then throwing your frizzy hair into the faces of those (i.e., me) behind you.
4. Talking and talking (and talking some more) during ALL of Modest Mouse. If the music is quiet enough to carry on a conversation, it probably means that said conversation will detract from others' enjoyment of the show.
5. Holding up those big face signs at just the proper level to block out as many people as possible. (The first 3-4 were mildly funny, but the 50th one I saw suggested a lack of originality).
Bottom line is jump around, twirl, spin, dance, shout, sing all you want but just respect others' space.