Definition of bullshit:
(n) :
blatantly false statements, generally made with intent to deceive; a
card game in which the object is to bluff about cards laid down and to determine when one's opponents are bluffing
"that's bullshit! I called your office and they said you never came in!"
"I think you're bullshitting. Let's just call your office and see if you even came in."
(interjection) :
an expression of disbelief at what one has just heard