XFrisk will probably react like most other people would, accepting someone as a new friend and treating them with kindness and respect, but he'll take it with a grain of salt. Too many times he's had things stripped from right under him, so if he gets too much emotional connection towards someone, he'll just end up regretting it in the end. While he's not as aggressive or violent as XChara is with rejecting people, XFrisk will still probably reject things silently. Such as, he'll make up excuses as to why he can't meet up with them when offered to hang out, or leave messages on read if sent any. He's nonchalant about being called rude for these things, too -- if anything, if he can persuade the other person to dislike him by just doing his normal routine, that's in his best interest, and what he believes to be the other person's best interest as well.
In the event that someone tolerates him through all of that and still is genuinely interested in him as a person, XFrisk will probably begin to be a bit more uncomfortable as to why they've still stuck around. His attempts to avoid them will be more blatant and, if he reaches a certain point of intolerance, try to even directly tell them to leave him alone. In the event that all of these still don't work and the person still tries to be his friend, he'll finally start to calm down and open up to them, but does so very slowly, in the event that he gets to close right when he loses everything again.
