Flong

Something you yell at someone if you think their story is exaggerated or you doubt its integrity.

(If you don't get the joke, Matt Rose posted a video recently about people saying two things and their brain mixing it into one - this person yelled "FLONG" at their friend because they were trying to say "That's hog wash" and "That's flim flam" at the same time)

"FLONG!"