When a Favor Becomes a Chore
Whenever people offer to do a favor for someone else, no matter what, it’s going to be slightly annoying. That’s why the person asking for the favor should be as least problematic as possible. Otherwise, chances are that the person doing the favor will drop out of their commitments.

However, that certainly wasn’t the case here in this particular situation. In what world is it appropriate to ask this of someone who is doing you a favor? Surely it shouldn’t matter what the caterer is wearing, especially if they do it for free!