Turns Out Babies Do Feel Pain, but Lobsters Still Don't. Source: Trust Us, Bro

At some point you have to realize the guy who wants you to prove the lobster does feel pain is a sadist. 

No, you sublimely evil Satan's-shitbag pet, if the lobster doesn't feel pain, obviously you have to prove it to me. 

Basically when someone argues that babies or lobsters don't feel pain, you should take it as proof that the arguer doesn't feel pain, and it should be legal to torture them for kicks.
"Prove to me you do feel pain and aren't just pretending, bro." *stab* "Hmm, I'm not convinced." *slice*