This requires two partners: a male and another male, or a male and a female. The giver will suck off the receiver's penis while the receiver is wearing a condom. This results in the blowjob being vegetarian as the meat is not actually tasted.
The same way that you lower the top of a convertible car to experience something different, a convertible blowjob is a similar process where a person removes the dental prosthetics and engages in fellatio.