Used to express amusement over jokes that at first glance seems unfunny, or makes no sense, but after thinking for a while makes you lol.
Humor that makes you lolwigi are often found funnier than normal humor that makes you lol directly, due to the fact that you have to have spend some time processing what just has been said or read. Another reason is that fact that you may feel stupid and left out at first, but when you finally get the joke you feel smart, and becomes a part of the group that understand the joke.
A: But I just had to. It was on $134.0
B: aahahaa! lolwigi
A: What's the best thing about fucking twenty three years old?
A: There's twenty of them.
B: ahh, lolwigi :)