Something you should definitely add to your repertoire of quirky sayings, but as long as you use it in the same snippy context as Eric Cartman of the show South Park. Also the only acceptable phrase containing the word "hella".
Person 1: Why are you wearing sunglasses inside?
Person 2: 'Cause I'm hella cool, that's why.
(N.) A term made up in Southern California by Gwen Stefani of No Doubt. It means "Super Duper Cool" and is most oftenly used by assholes and douche bags trying to be hip-dope-fly. Eric Cartman of South Park also use to like using the lame phrase, too, but forgot about it soon after he got into it.
Gwen Stefani says you can be "Hella Cool", "Hella good", "Hella fly", "Hella dope", or "Hella mad".