Why is Mei so hated?

I think she's to overpowered when i play overwatch but that's me

both positve and negetive, she isnt that great on high ranks and super power on low ranks .

Yeah in high ranks like Diamond+, she can be countered pretty easily by a McCree but in the lower ranks, players don't know how to switch heroes and handle a Mei. She is not overpowered just people don't know how to counter her.

idk who is exactly is mai but she or he must be someone bad to be hated

No experience required, you only have to freez and head shoot.

I think she is just generally a frusturating character to play against, not that she is overpowered but her abilities seem like they are designed just to be aggrivating.

He's one of the worst characters with his ice wall ...

she's definitely OP because of the headshot damage and she's hard to counter unless you're playing against someone really good. Most of the time, she's grouped up with Zarya and Symmetra which make whoever they're attacking completely incapable of doing anything but dying.

Stun mechanics are always hated, and the ability to freeze yourself to heal whilst invuln is really irritating.