I think you're making a mistake in assuming that there are set "rules" on this subject, but uh...
KevinLA wrote:
It is my understanding that if you lend something (whether it is money or a pen), you should not expect it back nor even ask for it back..
If we're talking tiny amounts of money here, then it might make you seem a bit miserly to ask for it back. The same is probably true if this pen was loaned out some time ago, but I don't think most people would object to you saying "would you give me my pen back after you're done with it please?" or somesuch before you give it to them, or a short while after.
There's no way, if we're dealing with a decent amount of money here, that you aren't to ask for it back, and if the person objects, then, frankly, humbug to them.
(these are just my impressions though, and, like I say, I think it's a mistake to think that there are anything so formal as rules to this)