tag questions

The first will be if you capitalise the initial I, put a comma after nice and close the gap before the question mark.

Anonymousi'm looking nice aren't I ? or ain't I?

I don't like either, although "aren't I" is spoken in conversation by some native speakers. Personally, to avoid making tag question errors, I usually say " I am a nice person; am I not ?"

AnonymousI am a nice person; am I not ?"

That is not natural for most native speakers. 'Aren't I?' is correct English; 'Am I not? is rather formal. In any case, the semi-colon should be a comma, and there should be no space before the question mark.

AnonymousI don't like either, although "aren't I" is spoken in conversation by some native speakers

Make that "by most native speakers". It's not an error: aren't here is just an irregular negative form, not a contraction.

Am is one of several verbs that change their vowel in the contracted negative - do, can, will, shall. Aren't is the only one that appears incorrect to some people because of the rendering of the vowel in the written form by 'are'.