I’m not much for breakfast, but if a diner has Corned Beef Hash, I will order it instead of trying to get them to make me an early sandwich instead.
I will almost always order French Dip if it’s available for lunch. If a place has CBH AND French Dip, the Dip wins.
Something I’ve never eaten before.
Something I would never make the effort to make at home. And I make a lot at home.
Foie gras, truffles, chanterelles, macaroni and cheese, spaetzle, brown butter, marzipan. No, not all at once, wise guy.
Duck, foie gras, pesto, mushrooms, spaetzle, or garlic&potatoes.
I’d probably be ordering it if a dish contained:
Artichokes
Avacodo
Asparagus
Capers
Crab
Cheese
Shrimp
Garlic
Lots of butter 
In a dessert:
marzipan, pistachios, blackberries or raspberries, custard and/or very lightly or unsweetened whipped cream.
A dish containing all of those however would not be very high on my list. 
And there are a few items on a menu that will make sure that I do not order at all (foi gras - the real kind- being one of them). I won’t patronize a restaurant that disagrees with my food ethics even if I am not partaking of the “unethical” food stuff.
artichokes, avocado, lime/lime juice, shrimp, noodles or noodle soup
Gorgonzola cheese
Feta cheese
Capers
Artichoke hearts
Sundried tomatoes
Portobella or other fancy mushrooms (i.e., shitake)
Duck
Lamb
I will second all of these as well–we could get along really well if we cooked or dined together–except that I have not had duck yet.
Oh shit yeah I forgot: I always order scallops. Don’t believe I’ve ever passed up a scallop appetizer in my life.
Cilantro!
in an entree:
Duck
Rabbit
Chanterelles
Sweetbreads
Housemade sausage
Foie gras
Pate
In a sweet:
Passion fruit
Panna cotta
Dark chocolate/raspberry combo
Avocado or olives
Cheesecake
(but only if the main I choose isn’t pork, as avocado, cheesecake & pork would be too rich for me)
Breakfast - eggs benedict - especially if made with smoked salmon. After last time though, I’ll ask for the hollandaise to be served in a separate jug.
Cannoli. Duck breast. Wine. 
Most other items, I’ll usually consider what I’ve eaten recently and what I plan to eat over the next few days. For example, scallops - I make scallops about once a month or so, so if I’ve just had them or plan to have them soon, I won’t order despite loving scallops. And, if I haven’t had them in awhile, sometimes seeing them on a menu might trigger a “I’ll make scallops this week” mood, so again, I’ll pass.
Yes! And +2 (3? 4?) on scallops. We fixed bacon-wrapped scallops on Sunday and they were awesome.
Also garlic mashed potatoes, or any mashed potatoes as long as they’re not instant potatoes.
Tofu in particular, and anything I love but can’t/won’t make at home in general.
I do love mashed potatoes (particularly garlic mashed potatoes) but they are so easy to make and I make them so often at home that I rarely order them. I will opt for the potato or side dish that I can’t recreate at home or that I haven’t had in a while (or won’t be having for a while).
I need to add scallops to my list too though…I am not sure how I left it off the first time, but definitely scallops…
Most shellfish, asparagus, foie gras (wasn’t expecting there to be so much foie gras love!)
Foie gras
Bacon
Artichoke hearts
Capers
Scallops
Game meats
Bluefish
anything in a mushroom/cream sauce
GOAT. I’ve never had a goat I didn’t like.
goat seconded
raw beef (tartare, carpaccio, kitfo, etc.)
tripe
shellfish
ama ebi (with the fried shrimp head)
Friday fish fry