I think Phayu started flirting with Rain for the "omg he'd out target, I dare you to make him fall in love with you omgomgomg-" Plus there's a relationship chart floating around that says {Boss = Phayu's Rival}.
Either Phayu is trying to get a 1-up on Boss or they have a completely different plotline later where Boss comes and flirts with Rain, [I have no idea don't keep me responsible lol]
Overall I think for Episode 4 that Phayu's gonna start acting cold towards Rain, "You shouldn't come here anymore," aka. the, "I'm ignoring you obvi," cliche.
Rain's gonna go off finally realizing Phayu's not wanting to talk to him and Rain's then gonna figure out his feelings with a deep convo with Sky. After Rain and Sky have figured out that, "Yes, Rain has feelings for Phayu." I'm gonna guess next that Rain will go off and try to talk to Phayu again, but get stuck in a similar situation to episodes 1&2 where he was in a risky situation and Phayu will have to save him. Even though Phayu's gonna be a jerk for the episode, he's also gonna realize he likes Rain cause he obviously does like Rain. Then the two will talk out their feelings and according to MAME's writing, they'll probably have boomchicabangbang.
That's just my guess though, lol.
[To anyone who's wondering why I keep throwing cliche around because that's MAME's writing style, she write cliches, but in a good way as we're all invested in it.]
