I eat at public functions a bit in my job, from conventions to meal based meetings.
Here's what I've noticed from the omnis:
they wait until the entire table has been served. Other tables are not priority.
They think the time between their yet another version of dried out chicken corpse arrives and whatever if anything that commie freak (read, the vegetarian) gets is the perfect time to quiz about diet or ask what do I eat. some mean really well and talk recipies. that i can deal with except i'm good at imagining what I'm discussing!
(Hello, I'm starving, you are eating and making me talk about food!
However, when I'm accomodated the starving veggie mentality has kicked in and I get humongus servings.)
this is a great reason to eat the salad slooooooooooooooowly and have two pieces of bread on your bread plate.
At a buffet, you are fetching your own food, so dig in, unless you want to wait for the table to be re-seated.
My spouse in omni and we often have our dinners staged differently. I wait, he encourages me to start.
I'll slip him some of my food.
My son is taught to wait, with an explanation of our family-specific practice.
When it's just us, we simply ask if the other one minds.