Haha too many to mention.
Notable ones that spring to mind:
Turning round and seeing my mate (who has a skinhead) with Bin Laden style beard and turban thing.
Swearing blind to my mate for several hours that a tree that was lit up by lights at a rave was in fact a metal statue of Bowser from the Mario games.
Plus the standard ones, ie holding conversations / hearing conversations involving people who aren't there, usually while having a piss.
Unable to read those old school green mobile phone screens.
Thinking people who've gone home are still there (ie. "Where's x?" "x went home an hour ago, you mug", etc)
I also used to have this thing for a while where I would get back from a club (one I used to go to every Friday night when very young) turn the lights off and jump into bed then, when my eyes got accustomed to the dark, the room would look like the actual club itself, only really dark, creepy as fuck, as I always half thought I was still at the club but just really fucked up.
The most disturbing one of these I ever came across was after giving an inexperienced user some very strong MDMA, he then turned round and asked me "where are we?" to which I replied "at (the club)". He then turns round and goes "I just thought we were in Belgium" and looks at me all confused. Had a worrying night that day I can tell you.
Does anyone else get that thing where, if you've been to a club with a real loud sound system and your ears are ringing, you can hear and make the most amazing music in your head whilst drifitng off to sleep? Awesome.