This is a mistake.

Depends. If you're talking about normal social functioning, sure, this is wildly sub-optimal unless you hang out mostly with debate heads or others who put a high value on quick wit, and superior argumentation skills. In any problem solving or intellectual arena it is an awesome technique, but yeah, outside of a pretty narrow group if you act like that normally it'll go down like a lead balloon. But presumably as one familiar with the Art of Charm guys you know that most social interaction is grooming/bullshitting/vibing where the noises you make with your mouth are important more for the way they're said than for their informational content.

On the ex-gf thing, tell them if they have a problem, say it immediately or you'll assume it doesn't matter. Repeat this policy whenever such stuff comes up. Works for me.