Why can't you just accept that I'm fine in this long queue, which is behind him, where he can't see me at all, which is why I joined this one in the first place? Here, let the person in front of me hop to that queue instead. Go away, please.
Is the cashier on this till due for a break? No? Then why the insistence that I should go to another till? The other cashier is a Nice Guy? That is your experience with him, not mine.
tl;dr, the person pointing people to tills with shorter queues wouldn't take "I'm fine with waiting a little longer, the cashier on that other till is someone I feel uncomfortable around", tries to get me to join his queue anyway.