The only way you should lend your bike to another is with the understanding that it might break, they might crash, it might get stolen & you're ok with dealing with it yourself. Otherwise don't do it. It's like lending money, don't do it unless you're ok with never seeing the money again. How else can you deal with it if your friend takes your bike & something really bad happens & he says he was just riding along? You see fault, he sees normal use. The frame was due to fail, he did nothing wrong. It's a great way to ruin a friendship, whether he replaces it or not. Either way, one party is pissed. Much easier to just say you don't lend your bike. But if you truly believe that a bike is just at thing and it can be replaced whereas a friendship cannot, then you lend it with the understanding that you may have to replace this thing yourself.