1. You know when you make that really inappropriate joke in front of adults if you're a teen and vice versa, that they really shouldn't laugh at so they just let out a single "HA!"
2. When you laugh at a joke that isnt that funny to make the person feel good.
(On a busride home)
Teen 1: Damn i have a lot of homework to do
Teen 2: Yeah I can't wait to get home and "study" (drug reference hand gesture)
Middle Aged Bus Driver: HA! (half laugh)