Carlos Mencia -- Comedy Is Harder When You Lose the Fat

Carlos Mencia knows that fat is funny -- and dropping 70 lbs can be a career killer for a comedian -- but this weekend, the comic found a way to make skinny work ... with the help of a little person.

A slimmed-down Mencia was telling us all about the weight loss at The Improv in L.A. ... when his former "Mind of Mencia" co-star Little Brad stopped by.

Mencia -- pointing to his pal -- told us, "We wear the same size shirt" ... adding, "I'll show you that I fit in a dwarf shirt now." The two proceeded to swap tops ... right in the middle of the street.

He added, "I don't know if this is cool or pathetic." Check out the footage -- you be the judge.