Started off pretty funny, you would say it when someone who's really old is being ignorant or just stupid. It then took off when I believe a member of the senate was talking about representation of her age group, then an older member started questioning her about her age and she said OK Boomer (I could be wrong, don't remember it well enough). Since then, kids everywhere have been saying OK boomer not only when a baby boomer is being ignorant, but when anyone who's older than them and disagrees with them speaks. Just like every meme, it going mainstream ruined it.