Let's losers think that the girl that hates them or treats them like shit likes them.
Or the brutal Hatefucking/pseudorape that will occur later.
Also let chicks who don't have the spine to be upfront about how much they like dudes to be a bitch and get away with it because true love or some such stupid bullshit.
Also, Mandy isn't a tsundere.
She's just a bitch.
All modern versions of the tsundere's are bitches, if you think about it.
But she's just..a massive bitch with no cause or reason period.
And that is the appeal of her.