1: the 'cool' way of laughing. The way Peter Griffin laughs in Family Guy.
2: Something Hootowls say. They say this because once, in a concert while performing "Alligator Sky", at the end of the song, Adam (if you do not know who this is, you obviously didn't click on Hootowl ) made an inhuman (adorable) noise that is believed to be spelled "Nyahaha".
1: Nyahaha, that's cool.
2: OMG I love Adam so much!!! LOL NYAHAHA
Laughing like a Japanese cat person also known as a "Neko"
Neko's are seen in Japanese Anime
Person 1: *Says a funny joke*
Person 2: Nyahaha!