lit. cut sleeve (idiom); fig. euphemism for homosexuality, originating from History of Western Han 漢書|汉书: emperor Han Aidi (real name Liu Xin) was in bed with his lover Dong Xian, and had to attend a court audience that morning. Not wishing to awaken Dong Xian, who was sleeping with his head resting on the emperor's long robe sleeve, Aidi used a knife to cut off the lower half of his sleeve.
Definitions (Wiktionary)
phrase, figuratively, idiomatic
male homosexuality