Loutish describes behaviour that is rude, rough, and badly brought up — the kind of thing a lout would do. A loutish remark talks over someone and makes them small. Loutish manners at a table might mean grabbing, shouting, or laughing at the wrong moment. You can say a loutish young man, but you can also say loutish behaviour, which is useful, because then you are naming the act, not stamping a person forever. It is an unkind, judging word, a little old-fashioned, more at home in British newspapers and novels than in soft everyday talk. Though actually, it is about manners and force, not about being large or loud as such; a quiet person can still be loutish if they are coarse and pushy. It is stronger than impolite and less formal than barbaric. You would use it when you want the listener to feel the ugliness of the behaviour.