Seeing a band onstage that is shitty, you know is shitty and yet you see everybody else around you losing their mind for such a shitty band. Makes me feel like I'm in the Twilight Zone and I think that I'm the only one hearing what is really going on stage.
Examples I can think of right off hand:
Odd combination and some might laugh. I went to a show in Springfield, MO about 10 years ago to see Andrew WK. Who come to find out didn't headline. The headliner for this show was fucking Hoobastank. I was not the driver so I had to sit through a goddamn set from Hoobastank before The Reason song blew up. I stood there hating life while I think I was feeling the floor moving.
Being at Rockfest in KC w/ 40k people going batshit crazy for Shinedown who I think I started hating even more than I did before, while I waited for STP to get on stage.
I'm sure I have more but those 2 always come to mind immediately.