When people get rowdy and trouble starts, you:

Ignore it and continue as you were, if possible.

Get the heck outta there, quickly.

Stick around to watch. ("Fight! Fight! Fight!")

Passively stick around to watch, but stay out of the way. ("Better keep an eye out…")

Immediately look for any excuse to get involved. ("Nothing like a good brawl!")

Only get involved if it sucks you in (i.e, someone threw a bottle at someone else, but it hit you instead).

Immediately get involved to try and break it up.

Only get involved to try and break it up if it starts getting out of hand.