Let someone else try giving your baby a bottle, or use a sippy cup on older babies.
First, have someone else give him the bottle while you are out of sight, or better yet, out of the house! This would be a good time to run a few errands so he knows you are really gone. Some babies will take bottles right out of the fridge when Mom is gone, so experiment with the milk temperature.
In an older baby, you might want to try a different vehicle such as an open cup or a sippy cup with a straw. The problem might not be the wrong nipple; it may simply be the fact that he doesn't want a nipple at all.
Remember, even though this is difficult to go through, when he gets hungry enough he will eat. Babies are smart enough to not let themselves starve!