lol (laugh out loud) -> lols (plural form of a loud laugh) -> lolz (cooler way of the same) -> lolzz (supposedly even more cooler) -> lolzzz.
Lolzzz is usually written, not spoken, but a common pronouncement is 'lol' + a long 'z' getting lower and quieter (like a landing jet plane). It can also be pronounced 'lol-z' with a very abrupt Z.
Lolzzz can refer both to something very funny or something not really funny.
A: My neighbour's cat yesterday saw a speeding truck and got scared half to death, ran up a tree and didn't come down until the next morning, isn't it funny?
B: Lolzzz. Poor kitty.