Is it true that in football (in the British sense) it's not against the rules to hang around the goal area but it is considered very bad etiquette?

The offside rule pretty much prevents that, in competitive football. You can't receive the ball if you're past the last defender in the opposition's half when a horizontal line is drawn across the pitch. That's the basics of it. So it pretty much prevents goal hanging, which is what we would call it.