LOL I have similar problems with my DS wanting to copy DD with various things eg a dummy...he never ever had one but seeing DD with one made him want one. And he likes to be carried like a baby occasionally while he makes "goo gaa" noises like her .

How about upgrading him from sippy cups to cups just like Mummy and Daddy use? DS now has a "cuppa tea" ie warm milk in a Bunnykins mug and he loves that...and I let him drink water from a glass and he looooves straws so I also have Tupperware cups that have a lid with a straw hole. I just buy normal plastic disposable straws at the supermarket and it is a big treat for him to pick which colour straw he wants.

Otherwise...give him a bottle with a slow flow teat for newborns and he might get so frustrated with it that he'll give it up again!!!