My Sim, Dirk, successful crashed a party one night. I got a pop up message saying something to the effect of "cool, no one noticed" and he stayed and partied until he got kicked out at 3 am.
The next night I noticed there was another party at Wayne Bumble. Had Dirk crash it. Instead of getting the pop-up, I got kicked out almost as soon as I walked in the door. The option to to crash the party was grayed out. So I went back to the building and used the call box. Wayne Bumble was like come on up to my apartment. Went up there, walked in the door and got kicked out again. A pop up said that I was not on the invite list so I had to leave.
I look forward to seeing my success rate on party crashing. I think it is fun.