Meaning:
"售罄" means "sold out," and "男" refers to "men." Originating from South Korean media reports, the term was first used to refer to ideal men in the show biz who had got married. Chinese fans of Korean TV shows and K-pop gradually accepted the term, which has then been used on common people who are not celebrities. While "sold-out men" can be an ideal love interest no longer available, "sold-out women" can refer to nice married women.
Example
A: 你们办公室新来的小李很不错啊，工作效率高，长得帅，还很幽默。
Nǐmen bàngōngshì xīnlái de xiǎolǐ hěn bùcuò a, gōngzuò xiàolǜ gāo, zhǎng de shuài, hái hěn yōumò。
Xiaoli, the new guy in your office, is cool. He's quite cute, efficient at work, and has a good sense of humor.
B: 这样的男生会没人喜欢吗？他是售罄男了。
Zhèyàng de nánshēng huì méi rén xǐhuan ma? Tā shì shòuqìngnán le。
You think no one has seen into the eye of such a guy? He's married!
(Edited by Stephanie Yang)