This changes things a little. I guess you have three choices in this situation. What you did (warn the guy), "rat him out" to the meter maids, or ignore (and therefore not do your job). Since you want to perform up to expectations at your job, the last choice would probably be out. I guess if you have a good relationship with the party, you would choose the first option. That doesn't seem to be the case here, the guy sounds like a major league tool to me... therefore the second choice would be a good one to teach him a lesson. I guess if you wanted to be really nice to the guy, you could tell him that someone with a h/c tag complained to you in the lot....this way you don't look like the bad guy and thusly avoid conflict.