My guitars, Never... I once loaned one to a guy, turned my back for 5 seconds, and there are no words to describe the sound I heard... when I turned back the headstock was haning off the guitar by the stings... Never again... no way... no how...
He was smart enough to pay for it, lemme tell ya... accidents happen, I just don't want them happening to my stuff in your hands...
Fellow musicians at sessions?? Sure... but I know them all, and I trust them all...{~`