to describe a certain substance or activity a person enjoys, and often practises, while said person morally believed or is informed that the substance or activity is abnormal, improper or incorrect.
See more at: guilt, guilty, pleasure
Trey: "Yeah dude that's a guilty pleasure"
You: Yeah! I know!
Your guilty pleasure: Sunday mornings Taylor Swift is turned up while you're cleaning your room... and you just purchased outrageously, expensive tickets for her concert.