What does the joke in the second episode of Days Related to Youth mean?

Are you telling that joke about the lame blind man?

The blind man carried the lame man on his back and said, "Did someone take a bath in the river just now?" The lame man was surprised. How do blind people know the answer? Because the lame man saw a woman taking a bath and had a physiological reaction. The blind man felt a change in his back. Ha ha ha ha. Then the dialect told Li Bailing that Li Bailing called them hooligans. That's very wise. Haha, I like that play, too. I also want to ask you something. If you know where there are old military uniforms like those in the play, please tell me. Thank you.