YEHET... 

according to Urban Dictionary.

1. Yehet is the sound that Oh Sehun, a member of EXO, makes when he is happy with himself. 
2. It is also the cheer of a 4-dimensional 19 year old who is allowed to make weird mating noises such as the word itself, "Yehet"

Sehun: *looks down into pants* 
Sehun: Yehet