If I recall rightly, in Air Warrior you could shoot down friendlies, but if you made it a habit you got flagged "Persona non grata;" essentially an 8 hour time out.
Yeah, I've done that. Even tried staying on same side and flying one well-known offender's wing for an hour, poaching his kills and flying thru his fire on purpose. He was angry and felt it wasn't fair to be treated the way he treats others. He's still poaching. Nothing changed, and i felt like a avacado for giving him an hour of my attention.