For customs or security, I completely understand letting crew in first...although I too have seen less-than-courteous crew and/or large groups of crew coming through together and wished there was a better way.

I *maybe* get it at a fast-food counter airside, although there I would expect the crew member to ask politely and *only* play that card if it's a tight connection and they need to eat quickly.

VAT counter? Um, no, I don't get that at all. I'd be rather annoyed if someone pulled that stunt there.