This is just my interpretations of all the different laughs you see on the internet (check out the chart at the bottom of this wiki page, its awesome heh), y'know, like the way my gang of buddies (originally from Quake and then into MMOs and all that) uses all this different stuff.
Heh: A chuckle, could mean there's some sarcasm involved in the previous statement, or it could just be one of those "chuckles of surprise," sorta like a snort in reverse, I guess, or something that wasn't quite funny enough to actually make you laugh out loud, I tend to use these to indicate a smirk or some kinda grin, too, 'cause I don't like doing *grin* emotes 'cause showing your teeth to people is considered threatening in some cultures and stuff heh.
Hehe: a short little cutesy giggle, an inch from a snicker.
Heheh: A double-chuckle indicates the previous statement was definitely meant in a sarcastic way (its not sardonic though, its all friendly, there aren't too many sardonic laughs that I know of).
Hehehe: a giggle that's gone to the banjo-playing toothless whiskey-stinking hillbilly geezer levels where its not so cute anymore heh.
Heheheh: A pot-head stoner chuckle, indicates marijauna is being consumed or possibly some other form of brain damage has occured (but usually its the pot thing, its just one of those things that people do on the internet when they're high, like the way they sit upright in their seats like old ladies and follow trucks on the highway at 25 miles per hour when they ain't on the internet heh).
Ha: Mmm, I dunno, I never use this one for anthing all by itself like that, but it kinda gives me the creeps, so mebbe I should use it for something.
Hah: An explosive Yul Brynner Hands on Hips kinda laugh, its more of a puff of cocky aggression or displeasure than anything that has to do with good humor (its almost always used as part of a gag and not in a serious way).
Haha: Traditional laugh, I usually only use this in dialogue or in response to somebody else at the beginning of a sentence (I dunno why I think you need to use this at the beginning of a sentence, I just do, I never use "Heh" to start a sentence for some reason, its just one of those weird things).
Hahaha: a laugh were you actually had to take a sec to compose yerself afterwards.
Hahahah: Same as Heheheh.
Ahaha: the Terrance and Phillip Laugh, or a laugh that actually makes you rock back in your seat a little.
I started using "ahaha" when I was playing EQ to remind myself that if I started typing a laugh with a merchant-type npc targetted he'd aggro on you and insta-kill you ("h" was the "hail" key, and "a" was the "attack" key, so you can see where the problems might arise with improper modal chat box usage while hanging out with yer jackass buddies heh).
I dunno how many chunks of levels I lost 'cause of that laughing shit ahaha.
HAHA: A nice big healthy laugh where you go a little too hoarse at the end to complete a full HAHAHA.
HAHAHA: the "might need to call an ambulance because I'm about to rupture an intestine" laugh, or a Generic Maniac Laugh, this usually indicates that several minutes passed while you were overcome by humorous vapors, adding extra HAs on the end awards something more comdedy points.
AHAHA: a sorta semi hysterical, semi-insane laugh.
Muahaha: Evil Supervillain or Mad Scientist laugh.
Mwahaha: Evil Dumb Monkey Boy On Rollerskates laugh.
Teehee: cutesy man-pretending-to-be-a-girl-on-the-internet laugh, when we do this in real life as part of a gag, we cover our mouth with our hand to imitate japanese school girls with good manners.
LOL: teh "Laughing Out Loud" Internets Dummass Version of Laff.
Laff: the "Internet Cool Guy Nonchalant Superiority Fighter Form" of LOL, its from the same weapons division that the the word "ghey" came from, its kinda like a rock-paper-scissors thing if there were no scissors and so the rock always loses, fortunately it isn't wielded much outside of the world of IMs and chatbox-type things where you can type a lot of little things like that without any punctuation and stuff.
ROFL: its Rolling On the Floor Laughing, but this one is never gonna go away because there really are those times when these four little letters are all you can manage to punch into your computer to explain your prolonged absence from the keyboard and the conversation and whatever as you struggle to regain your wits, its a lot like the Internet Version of SOS.
ROFLMAO: the "Extended Version of ROFL," I always think that ROFLMAOs are a little too contrived and not really spontaneous enough to seem as realistic and authentic and plausible as a good ole Life Threatening ROFL, y'know, I start to get a little suspicious that people are only pretending to laugh when you see one of these.
Kekeke: the "making fun of the koreans who beat our ass at the original Warcraft" laugh.
Ho: either a generic term for a girl, a prostitute, or a battle cry, depending on how loud you say it (not a laugh)
Hoho: the cheesy superhero version of "ah hah!" or a noise people make when they want somebody to stop moving (not a laugh)
Hohoho: the Santa Laugh, we use it to start a gag where we're gonna pretend to be a pompous know-it-all like Mister Science and shit too though.
Not too many negative laughs compared to the junk they got in that chart, but we were never much into wrapping up our hostility in some kinda cutesy subterfuge, and even when we were into that kinda thing, we preferred to get away with it for as long as possible and not do any blatant-and-corny moustache-twisting and stuff heh.