Let me agree with you while going a bit further: antisocial only means one thing, and it's what you just described.

People use 'antisocial' colloquially as a synonym of 'asocial', but this is wrong, and asocial is the actual antonym.

Antisocial is no more an antonym of social than antisemitism is an antonym of Judaism.

The primary definition in the Oxford English dictionary is "opposed to sociality, averse to society or companionship." It cites a usage dating to 1797. The secondary definition given, which you claim is the only correct one, similarly cites a usage dating to 1802. If the usage you complained about was ever a mistake, 200 years of usage means it is no longer.

Language is a moving target, and like it or not, the term 'antisocial' has developed a decided bias in terms of its meaning, which carries legal and medical weight.

You don't want to go describing other people as antisocial when asocial is what you mean, this thread illustrates that.

I joke with friends about this in fact, if someone says "ah I'm probably not going I've been feeling kind of antisocial" I'll ask them if they're planning to [redacted comment on America's violent culture in poor taste].

This is magnified by British use of antisocial, see ASBO, it's not worth trying to hold the line for two meanings when asocial is just sitting there being unambiguous.

> the term 'antisocial' has developed a decided bias in terms of its meaning, which carries legal and medical weight.

Not in American English, which is why the Americans here are so confused about this whole thing. In American English, "antisocial" means "asocial" and the other meaning is obscure. And "asocial" just isn't in the lexicon as an alternative.