Salah is pissed because he didn't start and Klopp took too long to sub him on. When he is about to be subbed on weirdo Klopp wants to do a handshake and a hug because his love language in physical touch and he doesn't respect people's personal space or boundaries. Salah is pretending like he doesn't see him (he does) and "fixing" his socks. Klopp barely gets a handshake from an annoyed Salah and takes exception to it because...gimme my hug dammit. Salah is peeved because, he doesn't wanna play stupid huggy huggy games right now. Klopp just couldn't let the snub go and though he was som distance away from Salah goes over to Salah and says something snarky to him. Tensions are already high, they start chirping, things escalate, neither wants to back down.