A really retarded sounding internet laugh. Usually used in sarcasm and over enthusiasm.
It is another word used when you have nothing else to say in the matter. TEEHEE! Often replaces lol.
Niga Higa (Youtube Comedian) has mastered the art of TEEHEE! usually combining it with a fatality of some sort.
Retard: Why did the chicken cross the road? To get to the other side.
*Niga Higa throws a massive green ball at a randoms head*
Niga Higa: FATALITY! TEEHEE!