The adverb of 'uncouth' — it describes an action rather than a person. Where 'uncouth' says what someone is, 'uncouthly' says how they did something: rudely, coarsely, without the manners the situation asked for. 'He ate uncouthly.' 'She laughed uncouthly at the funeral.' Everything true of 'uncouth' is true here: it is about polish rather than kindness, it looks down at the person from a position of good breeding, and it can sound snobbish. But add one more thing — 'uncouthly' is much rarer than 'uncouth' itself, and noticeably heavy in the mouth, four syllables of it. Native writers usually avoid it. They keep the adjective and rebuild the sentence: not 'he behaved uncouthly' but 'his behaviour was uncouth', or simply 'he had terrible manners'. You will meet it mostly in older books and in writing that is deliberately formal or arch. Recognise it when you read it; you will rarely need to write it.

粗俗地、沒教養地（uncouth 的副詞形）。中文多半直接說「他吃相很難看」「他很沒規矩」，不會刻意用副詞。這個字在英文裡也很少用，讀得懂就好。