Very cool, the most cool, and extremely cool. The word is a hybrid of the English adjective 'cool' and the Italian suffix '-issimo' for 'extremely, most, very'. It is pronounced 'cool-I-see-moh'.
A: Ey yo, Weezee, you dig my pants? Snotty said they was wack.
B: Snotty don't know shit, aight. They're coolissimo!