I suppose it depends on what part of town you're hanging out in.
A little snug is ok as you don't want them to twist or slip if you hit the ground. Will give you nice burns if they do. But they shouldn't interfere with your movement on the bike. You should be able to put your knee down without pinching or binding behind the knees, etc. They will stretch a little bit, but not much. If you have larger than average build for your height (i.e. working out a lot), you might want to look at custom made rather than off the rack.