Ever seen a large application (backed by MySQL in this case) where every query used exclusively left joins? Guess why? The guy deciding what db server to use only knows one join syntax, and it's LEFT JOIN. Doesn't grasp the performance issues. Doesn't care about the fact that it potentially returns different data. (You can always add "DISTINCT" to the SELECT clause.)

Oh, and doesn't see the need for triggers, stored procedures, or referential integrity constraints, because "real programmers" take care of all that stuff in their code.

Yes, he actually puts down anyone wishing for referential integrity checks as just being lazy. Woo!

(Nah, we don't find corrupt data on a near-daily basis. Why do you ask?)