I loan $20 to a guy that works at a food bank. When he gets his monthly allotment via a plastic card we go to the market and I grab $30 worth of food and he puts it on his card...
The thing to do is to agree to payback terms with something to make it interesting to yourself BEFORE you fork over the money. In the workplace maybe there is something you would like to know, somebody you would like to know about, access to something, etc... get that before you lend the money and then pursue the guy starting the day before payday for getting the principal back. Interest up front, principal paid back: anything less is disingenuous on the borrower's part, given that you don't have a collection agency.
I found in the workplace that there were quite a few individuals that would come in my lab and take whatever they wanted but when I went in their lab they wouldn't give up anything. They were really hard to deal with, they would get aggressive but I was doing martial arts, I'd just drop something really heavy on their foot and say "oops, maybe you shouldn't come in here anymore"... If they wanted to fight I was good to go, I never told them that of course... There was no way to discuss things with them, it's a mental illness level of thingy... obsessive people with long attention spans are usually cheapshit to the core, they give nothing and love to take..