We review each other's code before it goes in. If the team says they're happy to work with it, then I've fulfilled my obligation. I am literally not paid to write the best code in the world. In fact, the company gives bonuses for fixing things, so they are in fact paying me to sneak bugs in.

What you do though is, you leave a very obscure edge case unhandled, make note of it, then just don't tell anyone. Invariably someone will hit it exactly one day before you're scheduled to go live. Then just apply the fix (make sure to procrastinate long enough to simulate working on it) and voila! The longest I've seen an edge case go unfixed in this manner has been three years.

Though truth be told I'm not smart enough to add bugs on purpose, I just sometimes notice I've failed to address an edge case and ... leave it. If it turns out to be important - I can fix it when the fix's value is maximum. Half my day is spent fixing others' unhandled edge cases, so it's nice to have one tucked away for a rainy day that you know you can fix easily.