I once found a bug that I couldn't figure out from the code, so I started putting log statements that would print out the variables on screen (yes I have xDebug, but old habits die hard). Then the entire website didn't load anymore and eventually the entire container crashed.

It took me an hour to realize I was trying to var_dump an object from the ORM, resulting in a memory overload since there were like 20 related objects that recursively tried to load all the data in the database.

In my defense, it was friday afternoon...