Yikes, Seraphine, you've just mentioned something that may well be way more complicated than I had ever thought.
"he likes her,
doesn't he?" is definitely right.
I originally thought "no one wants to be baddie,
does he(she)?" should definitely be "no one wants to be baddie,
do they?" but then I thought it may depend on whether "no-one" would be plural or singular - according to dictionary.com "no-one" is a pronoun so I'm at a loss about if it's singular or plural. In addition there are usage notes on
"they" and
"he" which indicate there are grammatical problems in deciding what to use. In general, I think "
do they" would be the best choice (see "2. usage problem") at
http://dictionary.reference.com/search?q=they but whether it's absolutely grammatically correct could be doubtful.
Is anyone an English teacher here - my brain hurts.
Before I collapse in confusion...congratulations, Seraphine, you're now a brave Gryffindor! The Fat Lady will now let you pass.
[Edited to add: Apparently "no one" is an indefinite pronoun and is singular. There is some good information on this at
http://webster.commnet.edu/grammar/pronouns.htm which also mentions the grammatical problem]