when a boomer says something stupid and completely wrong you say this as a way to say "you are completely wrong but i don't want to waste breath on explaining something obvious that you won't even listen to"
boomer: VidEO GaMeS CauSE vIolEnCe
someone else: Okboomer
Brushing off an unneeded sentence or conversation with a boomer by saying "OkBoomer."
Boomer: Back in my day, we ate pie made of mud and laundry detergents, drank bleach, and broke into power plants, but people nowadays are saying that is not socially acceptable!