For a while we had a customer who would take us out to lunch on his tab - he liked a big meal and a lot to drink, and realised if he took people from the software company maintaining his company's system (i.e. us) then he could claim it all on expenses. And he was senior enough that nobody would question it.
Sadly it came to an end when it was found to be the main cause of projects overrunning, particularly fixing the mistakes caused by drunken and/or hungover programmers.
Biting the hand that feeds IT
