Depends... just a "friend"? Or a "true friend"?
Only got one true friend, and she comes over everyday... sooo, it's not like she can hide things from me.
If it's just a friend, I'd simply say "maybe later" or "nope"...
I trust a friend as I do a total stranger... because they're about the same to me.
I have to make sure that since this is MY STUFF they're talking about, they have to follow MY rules... and I have to make sure that I PROTECT MY STUFF from them...
I usually make a situation where they HAVE to return it to me, or a situation where I can keep an eye on them at all times...
...but if I owe them one, I'm more willing to let them borrow...
If you earned what you have fair and square:
Whether they asked nicely or command it from you, they have no right to "borrow" (take) it from you.
Unless of course you're filthy rich and most of your things are just shallow pleasures, then it's your duty to make others enjoy what you've "earned".