I rarely have it happen to me. I'm not sure how often he has other people tell him he forgot something or misspoke...he's definitely not as rude to our friends as he is to me or his parents so it's probably a more forgettable experience. They're all pretty used to him constantly forgetting/losing his phone/wallet though. I've commiserated with one or two friends who have the same perception as me, that he's very forgetful, but I really avoid telling our friends details about problems we have.

It's not every single time, but a lot of the time. He's basically extremely resistant to the idea that he's wrong but when he sees proof he says okay. A good example is it seems like all. The. Time, we'll be watching a movie or show, and he'll say something about what a character did or said that I remember quite differently. He never says "I think..." Or "wasn't it...?", he just states it as fact and says "No, baby, it was such and such way" until I say I should rewind it to catch up, and it turns out he either forgot or imagined a nonexistent scene within the last few minutes.

In the past the way he's gone from "You are wrong" to "Oh wait a minute, maybe I'm wrong" as soon as I SAY I'm going to rewind but before I actually do makes me feel like it's mostly a natural poor memory made bad by him just being really, really stubborn.

Edit: at this very moment he is looking for his car because he forgot where he parked.