One that sticks out? Hmm...
I should have never tried to holla at a college friend of mine. That L changed the entire friendship (which as far as I am concerned now, is dead despite numerous attempts to prevent it). Post-ether clarity is a huge plus, but damn...
There's others, I'm sure (like high school), but long story short, you miss the shots you don't take (there's a few of those in my life) but sometimes... the shots you do get the gumption to take will fukk around and be the wrong one.