Yesterday I had the sudden thought that we don’t say good-mouth as the equal and opposite of bad-mouth. We may compliment or speak well or highly of people, but we don’t go around good-mouthing them. Maybe we should.
Wikitionary and Dictionary.com trace it to a calque from an expression in a Mande language of West Africa, which entered US English via Gullah. Wiktionary also adds “Compare Japanese 悪口 [waruguchi] (“to badmouth”), which is a compound of 悪 [waru] (“bad, wicked”) and 口 [kuchi] (“mouth”)”. I can also think of Latin maledicere/maledico/maledictus (compare English maledict (rare), malediction), so if three such widely separated languages have a word for it, then surely it’s not uncommon. See also Latin benedicere/benedico/ benedictio and English benedict (not used in this sense), benediction.
But imagine that one bus driver drives carefully the whole way, while another starts a sign language conversation with a person sitting in the front passenger seat (which really happened some years ago). Which one am I likely to tell you about, or to complain to the bus company about (I didn’t; another passenger asked him to stop it, and he did)? How many large companies have complaints departments instead of compliments departments? Some websites allow the giving of feedback about how we are doing. I’ll guess that at least 90% of the feedback is negative.
Many years ago I saw a cartoon of one person complaining about everything to another, who is trying to interrupt. The last panel shows that they are at the complaints counter of a department store. See also Douglas Adams’s Sirius Cybernetics Corporation Complaints Department, which is “the only part of the company to still turn a profit”.
Online searches for good-mouth found oral and dental products and treatments. Searches for bad-mouth found those alongside the criticise meaning.
Coincidentally, while I was drafting this post, Browse TV Tropes showed me Accentuate the Negative, which discusses and gives examples of this. Accentuate the Positive is a song by Johnny Mercer and Harold Arlen.