A question of informal punctuation: How do you correctly end a sentence with 'haha'?

Is this a casual, toss-off comment? If so, would put it:

It's always bugged me, haha.

I tend to follow Terry Pratchett on the use of exclamation points: in my opinion, they help if you're working on a Mad Scientist or maniac interpretation.

But since this is Facebook or texting, I am not sure if it really matters.

Ending a sentence with ha ha is very informal anyway, so maybe it's a moot point as to how it should be transcribed, since grammar is largely irrelevant at this level.

I sometimes write ha ha or he he at either the begining or the end of forum comments, as an alternative to a smiley. I rarely bother with any punctuation before or after, because syntactically I see it as no different to a smiley.