My favourite instrument-loaning story is about kazoos:

Two friends of mine do a very funny dead-pan duet of Danny Boy on kazoos. They were asked to do it at a festival last year, but only had one plastic kazoo between them. Now, the "best" kazoo player in Australia (Mic Conway) was also performing at this particular festival, and though we all knew he had his kazoo with him, it was agreed that asking Mic to lend out his kazoo would be "like asking Yehudi Menuhin for a go on his fiddle". So the boys decided not to do their party piece after all. They were lamenting this in the bar, when Mic overheard and held out his shining brass kazoo and said "Hey - wanna use mine?". He was a bit perplexed when we all fell about laughing. The pair did their Danny Boy, and it brought the house down!

cheers
- Chicky