I work with quite a lot of musicians - a lot who play festivals, etc.
But my favourite most random situation happened at a charity event we were doing two years ago. I was up in the Production office, doing ma thing, and the work experience girl came up to me asking if I had a blackberry charger as one of the celebrities wanted to borrow one. Of course, I do, we have spares (for emergencies) but I joked around saying "yeah, well, they can borrow it but only if they're awesome. Z List doesn't count". About five minutes later, Rod Stewart appeared at the door and said to me "thanks so much for letting me borrow this, I always forget to charge it properly!" and just walked off. I think my jaw was sufficiently close to the floor at this.
Another of my favourite random stories was when I was working my first job at Reading Festival about 6-7 years ago, and I was working on the main stage, basically taking competition winners up on stage to see their favourite band play the first three songs or whatever. I can't remember which band it was during, but it was quite quiet, not many people had decided to go side of stage and I was just watching these two guys who were totally ecstatic and bouncing around obviously having the time of their lives (and to make sure they didn't run off) when this guy said in my ear "they look like they're having fun! mind you I love this band" and I turned around to like smile and say "yeah they're awesome" and it was Dave Grohl and I just went "YES." and I just turned right back round to the band and was like in complete oh my god state. I can't believe to this day its all I said to him. What a lame, lame thing to do. I totally freaked.
P.S. Sorry for any terrible english today, my brain is frazzled after a rather large panic attack this morning and I can't seem to focus properly :|