Jisho.org Forum

Probably there is no difference between the meaning of ねぇ and ねェ. But you should note that ねぇ sometimes refers to a long ね, such as いいねぇ (so good) or かわいいねぇ(so cute), but sometimes it also refers to ない, such as じゃねぇ=じゃない, いけねぇ=いけない.

Katakana is often used to emphasize the tone, for example, ダメ=だめ (no way), ブタ=ぶた(you pig), バカ=ばか(idiot), テメエ=てめえ (I don't know how to translate the word, perhaps "you asshole"?) You must be careful in using those words in real life, or people would think you must have read too many mangas.

テメエ I would think is closer in use to 'why you...', but with the same level as a curse word like asshole.

Hmmm... that sounds curious to me too, since doing a Google search returns slightly more results for なァ than for ねェ. It could be how the なぁ and ねぇ are being used. For example, some young people have a sort of high, nasally way of shouting things like スキじゃねェ！ I can't imagine shouting なぁ in a similar sort of tone. But then again, maybe the authors just don't like the shape of ア.