Unless you have the authority to do so, standing in front of someones bike and restricting their progress is impolite. He clearly moves into the path of people to stop them. He doesn't have that authority - simple.
I guess that standing in front of someone who is running after having stolen something in order to restrict his/her progress is impolite? Both stealing and driving/riding on the trottoar are illegal. Both are criminal offenses (the latter in case of a contact with a pedestrian) as per Indonesian law and obviously not authorized by any authority. It also definitely doesn't belong to Indonesian culture, so there are strictly no reason to be polite or patient with such people.
If I would be walking on the sidewalk and that an asshole rides it he'd better make sure that he doesn't touch me. If I am with family, especially with my kids, he has put himself in danger without suspecting it. I won't abuse him only verbally. I am reasonably confident that in such case, he may say that I am
impolite and more. All these asshole riding on the trottoar needs a good slap round the ear.
I don't give a shit about being an "expat" or not. I have been here for almost 20 years and am fluent enough to let know that if I don't feel I am superior, I also don't deserve less respect than Indonesian. Respect means, among other things, respecting my rights as a driver, as a pedestrian or whatever. Unless authorized by a formal authority, riding
my trottoar wouldn't go well if I need it to safely walk somewhere. I am not gonna go on the road. They will. Their behavior hasn't been authorized by any form of authority and they are not different from anyone stealing. Their attitude is also reproved by a number of Indonesian. Not all Indonesian show no respect for other's right, far from it.
They are not "progressing" or whatever, they are ENDANGERING the life of pedestrians and they must be stopped and told to get the fuck out of the way of those who have the RIGHT to be on the trottoar.
I am flabbergasted that some believe that only authorities should stop them. What's next? We should just call the cops when a wife beater or a rapist get into action? Sorry, I don't see it this way. In such case, I grab a club and give a taste of it to the wife beater. For a motorcycle riding the trottoar I intend to walk, potentially endangering me or anyone else, I won't club them but I'd sure tell them to get out of the way, and not in a polite way.
UU LLAJ is pretty clear and you should have a look at it to rethink your "impolite" bit.
Pasal 106
(2) Setiap orang yang mengemudikan Kendaraan Bermotor di Jalan
wajib mengutamakan keselamatan Pejalan Kaki dan pesepeda
Pasal 131
(1)
Pejalan Kaki berhak atas ketersediaan fasilitas pendukung yang berupa trotoar, tempat penyeberangan, dan fasilitas lain.
(2) Pejalan Kaki berhak mendapatkan prioritas pada saat menyeberang Jalan di tempat penyeberangan.
(3) Dalam hal belum tersedia fasilitas sebagaimana dimaksud pada ayat (1), Pejalan Kaki berhak menyeberang di tempat yang dipilih dengan memperhatikan keselamatan dirinya.
Pasal 284
Setiap orang yang mengemudikan Kendaraan Bermotor dengan tidak mengutamakan keselamatan Pejalan Kaki atau pesepeda sebagaimana dimaksud dalam Pasal 106 ayat (2)
dipidana dengan pidana kurungan paling lama 2 (dua) bulan atau denda paling banyak Rp500.000,00 (lima ratus ribu rupiah).