Nothing too bizarre for me. Last summer I turned to look at our keyboard player and when I turned back around there a flute player from the audience playing into my vocal mic. We proceeded to jam out and trade licks (he was way better than me!). My bandmates jokingly call that one Gris' 'Ron Burgundy' encounter, LOL.
But i don't have too many stories cause I'm not a real road warrior. I'd be in interested to hear some stories from some more experienced musicians than me.