Having a chimpanzee as a pet.
Saying, “Hey, watch this!” as you hand your beer to a buddy.
… while revving up the motorcycle/four-wheeler/four-wheel drive truck.
Also? Telling yourself “S/He’ll change, because s/he loves me.”
Jeans without a belt.
Buying anything from a guy wearing a jean-jacket.
Jean jackets.
Correcting spelling mistakes, in real life as well as online, never has the desired effect.
.
Trying to flick that bit of dust out of a wet paint job on a model–always a bad idea.
IME, it’s always a bad idea to quote corporate rah-rah slogans to your boss in crew meetings.
Well I am neither going to go apeshit nor call you names, but I will say there is a vast difference between a facial piercing, which can be removed with only a small scar, and a tattoo. 
Tattoing the name of your current SO - ALWAYS a bad idea. Tattooing his name on your neck? Even worse. (Yes, I knew someone who did this.) The only person’s name it’s acceptable to have tattooed is MOM.
Cussing out the judge.
Nah - I googled my gallbladder surgery - even watched a youtube video of it - and went under the knife with no trepidations.
So, I’d say you should qualify this with “googling your surgery within 10 minutes of having it done is nearly always a bad idea”. :).
Driving yourself to a license-restoration hearing.
Getting married as teenagers.
Dear God I used to play oboe back in Jr High and 1 year of high school.
My poor embouchure!
Having a baby to strengthen the relationship.
And, boy what a combo these two make!
Self trepanation
Self Surgery