When I was in the army, I once set my alarm clock for pm instead of am causing my roommate and I to be late to PT (physical training/exercise). The drill sergeants made us come to their office at lunch every day for a week to show them how to properly set an alarm clock ?

I once let my guard down, poured my heart out to someone that didn't deserve it. NEVER again!

Oh my goodness, I don't think I remember...

Don't tug on Superman's cape...
Don't spit into the wind...
Don't pull the mask off that ol' Lone Ranger...
Don't mess around with Jim (Croce)

Once I forgot that my favorite pair of short had developed a very big rip in the crotch at the rear, I put them on, walked up to the shop and only discovered my error when walking back by wondering why I had a very cool breeze blowing up against my bum.
I'll NEVER make that mistake again.

Where l hid my weed! l haven't forgotten since.

To leave my finger on the trigger of a nail gun. Ouch.