I dont understand when Mok said “to out him”? What does it mean?

I think because the brunette was saying that he would expose nanjo if they’re relationship came to a bust so I’m guessing it’s that

Remember when the twink wanted to hang out with Nanjo but he was busy so he told Mokyeon “maybe i should storm into his office and demand he fuck me or I’ll out him”

The brunette likes nanjo for his money and he has said that he thinks that rich ppl are snobby and he thinks deep down he’s straight if I can recall