Most Helpful Girl
Depends on the clothing type. I have tucked blouses into skirts and dress pants. It just looks more put together and professional when tucked in, but then again I'm skinny. If your girlfriend has a big gut then I think it would look more flattering untucked.
People still wear their shirts tucked (I see it everyday). As long as its not like a t-shirt tucked into jeans, which does look very geeky.