I was at a show in 1984 where during the Truckinn', Weir just kept REALLY flubbing the lyrics, until he finally just yelled "FUCK!" full scream.
Another show in Providence in 1986, the band was trying to segue into "Why Don't We Do It In the Road", but for some reason, Weir was stuck on trying to segue into "Gimme Some Lovin'". Phil finally yells " Do It in The Road, Weir!" The next night, before the second set ( it was April Fool's Day ), the crowd is doing the We Want PHIL! chant. Weir, obviously put out, maybe because of the previous night, steps up to the mike and says something along the lines of "Relax, you've got him. And take it from the expert, there's no such thing as an April Fool".
The last show in the summer of '86 before Jerry's coma at RFK Stadium in DC, where Weir introduces the band during the "( I Can't Get No ) Satisfaction encore was bizarre, to say the least. If you can find a good copy of that tape, it's pretty hilarious.
But, my all time fave, and it can only be heard on a good soundboard, was the second night of Merriwether Post in MD in 1985, right before the Stagger Lee. A girl ( that I and all my friends actually knew, although she still denies it ) was down in front yelling "Spit on me-eeee, Bobby! Bobby, I want you to spit on me-eeee!" The reactions of the band can be heard on the board as clear as day and they are funny as hell. Phil is trying to egg him on to do it, while Jerry is just like," That chick is telling you to SPIT on her, Weir".
Out of the loop? I didn't know there was a loop!