What does 토설 (吐舌) mean?

토설 (吐舌) literally means "spit/vomit (吐) [one's] tongue (舌)," but it seems to have been the Sino-Korean equivalent of 혀를 차다, which usually translates as click one's tongue, a sign of disapproval in Korea. The sound associated with Korean tongue-clicking is 쯧쯧, which can be placed in front of 혀를 차다 in written Korean for the onomatopoeic effect.

I used to hear a lot of tongue-clicking, or teeth-sucking, in the 1980s when I would walk down the sidewalks of Korea past a group of Korean men, usually older men. The clicking or sucking was so exaggerated that I suspected it was done to show their disapproval of me, a foreigner walking down their streets. By the time I left Korea in 2010, I hardly heard any tongue-clicking, possibly because by then there were so many foreigners walking the streets of Korea that it would have been a burden to try to click at all of them, or more probably because Koreans were just more accepting of foreigners by then.