Returning the wrong type on purpose
There is a 3rd party application we put scripts into from time to time - it's a pretty good app on the whole, but these scripts have to be VBScript.
Anyway - I pull data out of a database to use in these scripts, and have recently found that I have had to tell my query to return numbers as varchar. The reason? Because when I try to use CLng on the data (which I like to do in non typed languages), it complains that my numbers are bigger than 2 billion. So instead I'm putting more functionality into my query, and doing my subsequent maths there, returning the data as a pre-formatted varchar ready to just get printed out. I feel dirty and have to go home to wash.