Learned that lesson long ago. I always keep an inexpensive Mora or similar blade in my gear when going out with others.

However, what in my opinion is far worse that lending a knife is to see what other's have done with axes. I will never, ever lend an axe out again. Ever.. They will either kill your axe or themselves..

Did you ever notice that the more experienced the crew you're with, ie people you would lend your gear to, the less often that is requested?