Some chams will just refuse to eat certain things, try other feeders to widen the variety at meal time. Silk worms and dubia roaches are great daily feeders.
Haha, he doesn't like being constipated. Apart from mealworms not being too good for a chameleons digestion, I have seen that many chameleons simply would rather eat a cricket over a mealworm. They probably don't taste very good...