If they're round my place, with me in the room, I'm happy for anyone to have a go (5 year-olds, whatever - parents get scared, but I say "if she dings it, it's my fault". I do have a rather clumsy nephew, who can actually play, when he gets over-excited I rely on his mother's "carefull!!!" attitude to get him off it again :lol:).
I'd also probably be up for someone using one of mine for a jam round my place.
BUT - no way does anyone use one of my guitars in anger (a rehearsal or a gig). Even if they don't hurt it, a guitar always feels different somehow after someone else has performed with it. It's like you've gotta re-teach it how to behave...
And Dmoney, would you really lend someone a johnny? I might donate one, but I wouldn't want it back again! :lol: