My birthday is also coming up, and I do whatever the heck I want

. If I want to eat nothing but junk or nothing but salads that's what I'll do.
A couple suggestions to handle food pushers...
Jokingly say "It's my birthday, right? So I get to do what I want, and I don't want to order dessert."
Or
If they simply refuse to listen, order dessert and don't eat it. When they ask you why you're not eating it tell them "Because I didn't want it." When they ask why you ordered it, tell them "Because you insisted." Not exactly the most cordial way of handling it...but I'm sure you'll make your point.