You should never expect a reward.

You should always give one. Claiming it's an "insult" to thank someone for going out of their way to do something they didn't have to do (v. doing nothing or throwing the wallet out) sounds like an easy excuse to be cheap.

If you need any reward to do what's right you might need to search within yourself what kind of person you really want to be.

Then you are a cheap skate on the cost of other wallet loosers.