So right before the swat team busts through his doors, he strips naked with nothing but his daughters bracelet on. Why did he do this? The police walked him out with pants on, so what was the point?
Given the severity of the video Clyde sent Nick, Clyde is fully aware that the SWAT team will show no hesitation in opening fire on him should he not be fully exposed and defenseless when first encountering each other.
And, not only does Clyde strip naked, but he also walks to a specific place of the room and faces the door that the SWAT team will be entering. At this point, he's bare naked, in the middle of the room with nothing immediately around him (you can see that he's pushed tables away, and stands in the center of it all), and is directly in front of the SWAT team upon them entering.
By doing this, Clyde is removing any potentiality of him being fired upon by most explicitly showing that he has no weapons on or around him, and has no intent of resisting arrest.
From the screenplay of the film, obtained from IMSDb:
He stands. Calmly moves to the middle of the room. Kicks off his shoes. Peels off his shirt and undershirt. Even takes off his pants. There will be no confusion about hidden weapons. He positions himself, very precise and purposeful. Lifts his hands high above his head. Presenting himself. Waiting.