Which ones of the B sentences are admitted in spoken/written English?
A: I don’t like this sitcom.
B1: I don’t like it either!
B2: Neither do I.
B3: Nor do I. (Especially in British English?)
B4: Me neither.
B5: Me either (Especially in American English?)
All are possible. I use all of them. B5 would be acceptable in spoken English only.
I think B5 is American only.