"The Man Who Tasted Ashes", a short story by Algis Budrys, first published in If, February 1959, available at the Internet Archive. Does any of these covers ring a bell?
Short story about an unpleasant character
He gestured toward the bureau top. "Pour me some more of that." Alcohol affected him swiftly but not deeply. Once it had stripped him of the ordinary inhibitions, he could go on drinking for some time before his intellect lost its edge. Since he always took two aspirins and went straight to bed at that point, it was not a serious sort of weakness. But without his inhibitions he was a very unpleasant man.
who claims that he acts the way he does to attract first contact with aliens.
"All right," Redfern said sharply, "we've already settled that. Let's let it be. I don't care where you come from—I don't really care what you're made of. It may surprise you, but I've thought for some time that if people were coming to this world from other places, they'd be bound to get in touch with me sooner or later."
"Why on Earth should we try to get in touch with you?" Spence asked, nonplused.
"Because if you people have been coming here for years, then you're not here openly. You've got purposes of your own. People with purposes of their own generally come to me."
Charlie Spence began to chuckly. "I like you," he laughed. "I really do. You're a rare type."
At the end of the story contact is made with the aliens and they are captured by government forces. The main character claims that his life and character have led to this moment only to be told by an acquaintance that he should acknowledge who and what he is.
The Secret Service man at the base of the ship turned his head in Redfern’s direction long enough to show his exasperation. Then he pointed his pistol up at the man in the lock. “Jump down, you.”
There was the sound of someone heavy coming toward them through the brush. After a moment, Farleagh said: “There you are.”
“Hullo, Dickie.” Redfern grinned at Farleagh in the spottily reflected light. “Now you know.”
“Know what?” Farleagh asked heavily.
Redfern shifted his feet nervously. “Why I got myself cashiered years ago. You see I knew they were coming here — at least, I believed they were — and I decided
what sort of human being they would be most likely to contact.”
Rage crossed Farleagh’s face at last, and shocked Redfern. “Stop it, Redfern,” he said savagely. “For once in your life, admit you’re the sort of man you are.”
After that, no one seemed to look at him. An improvised ladder was brought up, and Secret Service men went into the ship and came down again escorting sullen, blue-lipped men. The clearing became full of activity as the prisoners were handcuffed together, machines and records brought down out of the ship; and Redfern watched it all, just as he had been watching all his life, from the outside.