The act of judging someone based on actions done, or events occurring, in the past. Retrojudging is not cool. Not cool at all.
Guy A: fml I'm gonna fail my chemistry exam...
Judgy little girl B: (in whiny "I told you so" tone) that's cause you skipped all your classes!
Guy A: stop retrojudging me, that's a thing of the past! Not cool.