I was playing a professional theater gig in Philadelphia. Even though I was 19, I didn't drive yet. There was a rehearsal on the afternoon of the first day, before the show that night. My dad picked me up, and took me out to dinner, to celebrate how I was now a real professional musician.
On the way back from dinner, he miscalculated the distance to the theater, and dropped me off 2 blocks away. I hung out by the back door, and decided to smoke a cigarette (I figured my dad had gone home to NJ directly). He did not know that I smoked. So there I am, being cool, having a cigarette by the back stage entrance, and who pulls up through the alley next to the theater? That's right, my Dad. He only said "drop the cigarette, we'll talk about this when you get home".
Having my dad catch me smoke was disasterous. I messed up so bad that I mis-tuned 2 of the 4 strings on the bass (my dad had let me borrow his 1964 Fender Jazz, which made everything worse), and didn't realize it was mistuned (all the way through sound check) until the opening number, where I quickly tuned it correctly.