A beggar's dozen is one short of a dozen and two shy of a bakers dozen.
The number 11 (eleven).
That jive talking cat short changed me. I asked and asked all week and he finally agreed to give up a dozen of them things but he only gave me eleven. When I asked him about it he said, "Well that right there is a beggar's dozen my boy. Beggars can't be choosers, don't ya know."
Basically the same meaning as Bull-Shit, but far more socially acceptable.
Everthing you said was a lie. I can not believe it. Your whole life is total bullwicky.