I walked in on my best friend and...
What did you see when you walked in?
He was buck naked.
I know it may have been an accident but you need to be careful not to invade people's personal privacy. I'd recommend apologizing to your friend because it seems like it was an accident.
My best friend told me to go in there, I'm gonna get him.
I am sorry he did that to you. He had no right to trick you into seeing him naked.