Pronounced "hi-you-sip". Orginated in emails amongst friends trying to fool work email scanners when swearing in text. Bad words are typed backwards to disguise them, so they can be sent through without being blocked. Pussy becomes yssup. When actually pronounced, it sounds like "yousip". When said over and over it began to sound like the fireball sound Ryu makes in famous Streetfighter game. The "HY" sound at the beggining completed the sound effect. It provides men a verbal way of pointing out hot women in mixed company without anyone knowing.
4 guys sitting at a table in a restaurant with their wives. 1 of them sees a hot woman walk by, and says Hy-yssup! Thus letting the other men know to look around to check her out, without the wives knowing.