Get fitter so you can beast mode it up the hill on the road and not worry about the traffic behind you.
Use your judgment I'd say. If it is a busy, fast road with few houses and would be appropriate for share use just not marked, then perhaps it might be acceptable for a short distance. You might be safer on the road than you really think though.
Regarding pavement cycling in general, yes it does piss me off when people do it when I am walking, especially ninja cyclists and ones who ring their bell at me expecting me to jump out the way. The fact is pedestrians aren't as focused on the act of travelling as motorists and cyclists. Pedestrians are on their phones, texting, carrying shopping, daydreaming, young and old, some much slower than others, jogging, pushing prams, on scooters. They aren't in the same mindset as road users, they don't do shoulder checks or walk in predictable lines. It's not a place to be cycling in general, and that's even before you weigh up the potential of drivers reversing out of their drives not expecting you to come whizzing past where they can't see you.