I agree the raid was just for drugs. Kay wasn't caught doing anything illegal.
We know he was drunk but that's not illegal.
The big surprise was that he was gay.
The reason why I think he wanted people to know, is because I thinks it's logical.
He knew that the raid would be that night. He went to that bar exactly that night on purpose. So he knew he would be "caught".
The logical consequence of being caught, is that people will find out he is gay. So he wanted them to find out.
As I feel it and as I see Kai, it is something he would do. I think he wanted to provoke, which fits to Kai.
Watch his face the next morning in the classroom (the end of the scene). He look on this face was not devastated or ashamed, it seemed to me there was a kind of pride (like: that's how it is, take it or leave it).
Why he did it, we don't know and is open for interpretation.
How I feel it, it's hard to explain, he wanted to force or provoke something. He just couldn't let it happen: Marc dumping him and thinking now everything is normal again as if nothing happened. So Kai threw a bomb. He is just not the type you can dump nice and quietly. And...if it was his intention to get attention, he succeeded. Because a little while later Marc was sitting in his appartment.
Now I think of it, maybe this whole thing was only to get Marc's attention. (Remember his question at Marc: is this all you have to say?).
But...of course this is only my interpretation. I see Kai as someone who doesn't allow anyone to ignore him.