A computer scientist's wife asks him...
A computer scientist's wife asks him, "would you pick up a loaf of bread at the store, and if they have eggs get a dozen?"
He gets home, throws 12 loaves of bread on the counter, and says "they had eggs".
This joke assumes is making fun of the software engineer. Apparently the software engineer did not understand that when his wife said "get a dozen" the thing that he was supposed to get a dozen of was eggs, not bread. The ambiguity of English allows this parsing of the sentence to be possible, but the humor is in the fact that no reasonable person would parse it in that way.