OMG the same thing happened to me!!!
I bought Sasha some cotton casual khaki pants in the summer, because his other ones don't fit him anymore. I washed and dried them on high heat, assuming that would cause maximum shrinkage, and then pinned and hemmed his pants. He tried them on, they were perfect, and then we threw them back in the wash to get the crayon marks out of the bottom.
The next week, he accused me of hemming his pants wrong.
Um, what does he take me for, an idiot? It doesn't take a rocket scientist to hem pants, plus, he TRIED THEM ON AFTER, so why all of a sudden is it my fault that the damned pants don't fit?
I still have the 4 inches of fabic I cut off from the bottom of his pants, now I have to reattatch the part, and make a hem that doesn't look too obvious... *sigh*