For eating at people's houses: usually people will have enough side-dishes that if one does not make a big deal of it, one can fill up on non-meat dishes. At worst, there's always bread.

For going to steakhouse -- yes, but at every other place, there's usually a vegetarian option, if one tries hard enough.

It does make a good case for being an unannoying vegetarian...but being a strict-vegetarian is a useful Schelling point.