As a Private: crack in a cylinder doing T&G's

As an Instructor:
2 engine failures, in a 172, on the same flight
door popped open in a 310 with an MEI student...he hung on for dear life while I took the controls and diverted (yeah, it wasn't pretty...)

As an FO:
knock on wood, only thing that's made my stomach uneasy so far was a "Service Door" caution msg at 200' on the T/O