It looks to me like May and Momo are BOTH seriously crushing on Sven.
May speaks fluent vulgarity and is very confrontational; but she's going to a whole lot of effort to keep his attention here, and starting with a challenge like that is an often-successful way of flirting. Sven probably has the experience to know this. It looks to me like he's sort of egging her on by rising to the challenge, which is also an often-successful way of flirting. Without knowing more about May's past, I don't know whether she has the experience to realize this or not.
But if I made bets, I think I'd bet that right now May has a better chance of getting with Sven than Momo does.
Poor Momo on the other hand is seeing it as a fight where May is behaving in a completely unforgivable way toward Sven, and she's just mortified to be in a situation where her crush is going to judge "May and Momo" for something she would never, ever, not in a million years, have done.
And if Sven and May do get together, look for Momo in either serious angst or the first really uncontrolled rage of her life, out of jealousy.