You're tooling around at 2k on auto climb, and some guy at 550mph comes in from 15k and nails you even though you attempt to evade.
It's a pick.
It's a (often) skill-less manuver designed to reward via instant gratification with no danger, threat, or effort towards the picker's part.
So you're wrong. There can be "picking" when only 2 are present, and NO, a pick isn't "only" when the picked pilot was on somebody else's 6 oclock.
However, we are in agreement that too many people throw the term out, like the newbies saying "Nice HO" to a 3 oclock glancing shot, etc.