Interestingly enough, I use "Haha" to denote sincere laughing. Mischievous laughing goes as "Hehe"; imitating an overweight person goes "Hoho" and normally imitating a timid person (or a woman, and I swear they are not related!) goes as "Hihi."
I'm 32.
Also, "hehe" means "only mildly amusing, but I'm not busy so I'll keep talking". (Unless you say "hehe" after something you wrote yourself, in which case it's creepy.)
I'm 29.
Or a ham radio operator, HI HI.