Judas Iscariot was with the disciples when Jesus washed their feet. Jesus could have waited until Judas left, but he purposely included him. By doing so, he taught us to love our enemies and to serve those who persecute us (Romans 12:14, 17-21).
We cannot determine to do this by our will power. When we are faced with that kind of situation, it is a signal to call on God for help. The Holy Spirit will then give us the grace and discernment to know what that service should be and the strength to fulfill it.