A. "Wack" somebody.
B. Make sure the bastard looking at your wife/girlfriend never again sees the light of day.
Cement shoes often consist of large block structured cement molds that fit perfectly around one's feet. The person sporting these trendy accessories is then thrown into a river, lake, ocean, or off of a bridge. Cement is used to asure the hitman, or average John that decides to murder his neighbor for having an affair with his wife, that the victim of this act does not float back to the surface.
B.) Bob: *walks in on his neighbor Harry having sex with his wife Martha* Hey pal, why don't you come out back, I got a pair of cement shoes in your size.
Harry: Why certainly Bob. *whispers to Martha* Even if I don't like the shoes I'll act like I do
*the two men go out back and a clank sound oddly familiar to that of a shovel coming into contact with a human skull is heard*
Harry was never seen or heard from again. His body was never recovered.