[ux266478]

> That sounds more like irony than sarcasm

I only mentioned forms. They're sarcasm because they're explicit mockery. I've read plenty of foreigners in Japan who comment on how it's weird they won't get praise from their boss in certain contexts where they expect it. This is a shadow of the killing-complement. Praise isn't issued because in that context a Japanese person would get the same sense that you would if your boss said "Good job!" in a baby voice.

> sarcasm as something quite unfunny (and also socially .. deficient?)

Probably because it's insulting someone to their face without just outright insulting them, often with the desire to cause offense (but varies in degree depending on your relationship with the person and the general situation). It's the same thing here and there, up to and including making everybody else in the room uncomfortable. It's simply manifested in a different shape.