RPGMemes

Ignoring the actual rules and mechanics is basically step one in almost every "isn't this goofy" D&D anecdote.

Not only is it not "decent damage" (even the buff it got in 5.5 just brings it from "the worst" to "poor"), it's also not a subtle thing you can just drop on someone unsuspectingly.

Spellcasting for an attack is an obvious aggressive action, which means an initiative roll comes first to see if you even manage to get it off before they clock you. It's also not like everyone around just shrugs and lets you go about your business because all you did was hurl an insult. You attacked someone with an offensive spell, the response is exactly the same as if you threw a firebolt at them

The flavor of insulting someone to death is fun, I'll grant that, but there's nothing special about Vicious Mockery mechanically that makes it immune to initiative order or people noticing what you're doing.