In the episode where Homer joins the Naval reserve, watch carefully at the part when they shave his two hairs. Right after it, he's holding the two hairs in his hands and sobbing, but if you look at his head, there are still two hairs there!
They had been at the naval reserve base a while for basic training. Remember they had already graduated at this point. Also, Moe manages to grow his hair back by the time they are on the sub. So, growing two bits of hair should be a breeze.
Actually, if you notice, the hairs that are on his head are not even half the length they were before it was cut. Hence his hair was cut. This is not slip up.
Dear Scolman,
By the time they were on the sub, they had gone through months/weeks of training. Of course Moe would've grown some hair back by then. The point is, Homers hairs grew back INSTANTLY!!!!
Hey you know what when homer shaved his beard in the "killer babysitter" episode it grew back in seconds its a joke and well if he can do that then he can grow that hair back very quickly
This is not a slip up. Just look at all the episodes in which Homer shaves. Within seconds his 5 o'clock shadow has fully grown back. Its supposed to be a joke.
Of course Homer's hair grows back fast! Remember when he was shaving for his night out with Marge? He had just finished shaving and then puts the top back on the can of shaving cream and his beard pops right back up. It's another one of Homer's little quirks!