The unit is correct. You can think about tits for as long as you want, and the human brain uses less power while doing so. Here's some improved wording:

The human brain uses 12W while it thinks about tities whereas AI doing the same thing uses 2.7 GW.

The major change was from "to" to "while", and I would argue that those words can actually mean the same thing:

"A person uses 100W to ride a bicycle" means the same thing as "A person uses 100 watts while riding a bicycle.

So, I would conclude that the meme is fine.