I wouldn't say it's impolite necessarily, but it is very casual/informal so I personally wouldn't use that term with a stranger.

You may use the term 'scooch over', it falls under colloquialism as it is casual or informal. You may also say 'please move up'.

Are you asking if you can say this to a stranger? Such as a person on a bench in a park? No. Definitely not. It is far too informal. The only person you could talk to in this way is a friend or family member. It would sound very rude to say this to anyone else. If you'd like a stranger to make room for you, on park bench, bus seat or on a plane for example, there is only one expression which is acceptable, and that's "Excuse me". Look at the seat and say "Excuse me" in a polite tone. That's all.

If it is an informal situation , sure!

Thank you