pffffft...... is like a shucking scorn.....simple translation would be "yeah right".....
say it P-F-F-F-T.....
like if someone came up to you and said, "hey holly, I heard you got gangbanged at the the timmy show on wednesday by 4 guys and Todds cat".....you might retort, "pfffft....it was only 3 guys and a stuffed teddybear"