In the time of Jesus, showing the bottom of your foot to someone was a sign of contempt toward them. Judas, in betraying Jesus, no longer considered Jesus his Master. Judas had committed to the service of new masters, the Sanhedrin. "No man can serve two masters. He will...be attentive to one and despise the other" (Mt 6:24). Therefore, Judas despised Jesus. By eating the Last Supper with Jesus, Judas showed the greatest contempt for Him (Ps 41:10), even if he outwardly appeared sociable.
When you break bread with Jesus at Mass, are you coming to serve Jesus as your Master? Do you have His interests in mind? Are you listening for a message from Him? (Jn 13:16) Or do you come to Mass while serving someone else, such as yourself? If you are serving anyone else but Jesus, you'll eventually love them and despise Him (Mt 6:24). Others may see your Mass attendance as respectful, but that's not what Jesus sees. He sees the bottom of your foot raised against Him in contempt (Jn 13:18).
How do you spend your prime time? Your answer tells you what you serve. If the answer is not Jesus and His interests, repent now. Give up all that you have to gain Jesus as your Treasure and your Master (Mt 13:44). When you humble yourself and accept Jesus as your Master, Lord, and Savior, you paradoxically discover who you are (Mt 10:39). "Once you know all these things, blest will you be if you put them into practice" (Jn 13:17).