It is worth noting! As you proceed, you now can have a /few/ interactions with him which are at the very least 'not negative'. He's still definitely being cocky, but he's at least /more/ amenable to talking to you.
Makes me feel like there might be /something/ akin to, if not a relationship, at least just friendship between the two of us, haha, despite me being firmly a top.
Unrelatedly, I have been told that at this point you can have a very different relationship with Gunnar if you /are/ a bottom or are female. So if goal was 'Friendship with Gunnar' or at least 'Not Enemies with Gunnar' then there are two potential paths to that, haha.
(Of course, if the goal /is/ 'Enemies with Gunnar', that one is easier if you can beat him in a fight)
The main thing is that if you beat him in a fight, be sure you /don't/ penetrate him. Mutual masturbation is fine, just 'do not get a black heart'.
Then besides that, it's just 'generally don't be a huge jerk to him', even when he kind of deserves it. When he insults you, roll your eyes but don't necessarily snap back. Help him out when he needs some herbalism while building up Bareshade. Don't tell Torben about his duplicity.
The meetings, I will emphasize, are not particularly 'friendly' yet haha, just a lot less hostile than they were at first. He's mellowing.
...now if you're a bottom or female, another option is to just cooperate with him and let him be in charge, in which he will presumably be a lot happier with you quickly haha.
Just make sure you don't get a black heart with him and hey.