I think because Barrel doesn't call you a bitch or whore all the time and he likes it if your'e a power bottom for him, not like Gunnar.
I think it has more to do with the fact that Barrel feels organic like he is a jerk but that's how he is and that's it, but Gunnar feels kind like that one overacting kid on that one school play you did, he feels like he actively diverting and exaggerating specific traits of him in order to keep us at arms length and of course he's a jerk all the way who doesn't know how to separate bedroom dynamics from everyday life(not like Barrel does that either, but even if he thinks I'm a bitch he's somewhat respectful (?), Maybe I'm tricking myself into seeing something that's not there), but yeah I dislike Gunnar mainly because he feels fake and exaggerated to me, like on propose to keep a distance from my character, and I tend to respond in kind, generally if someone is aggressive I'm aggressive in kind, so there's that.
Wow I didn't think I would write such a long explanation as to why I dislike a fictional character today but, whatever...