How do you know someone is a vegetarian? Don’t worry, they’ll tell you.
Just kidding, most vegetarians I know are really cool and non-judgmental about others’ eating habits. I’ve actually reduced my meat intake just by hanging out with a vegetarian friend that always went out of their way to make me something with meat when we ate together, and to return the favor I would always make vegetarian dishes when they ate at my place. And then I just sort of got into the challenge of making tasty veggie dishes! I would say I’ve halved my meat consumption over the last year because of it.