an exclaimation, mean "as if" or "yea right" or "get the fuck outta here" used in a loud manner usually with a feeling of offendedness;
1 Ken - hey Herbie, are you going to the middle school dance even tho you are a freshman now?
Herbie - Pwellt!!!
2 Phil (phone convo)- yo, Kenny, you need to come pick me up before you go out to the bar tonight, you owe me one
Ken - (not owing Phil "one") Pwellt!!! I don't have to do anything