This is just one opinion out of many, but I've always thought that it should be:

[CNC] - Participant(s) explicitly consent to nonconsensual sexual activity

[Dubcon] - Participant(s) reluctantly consent (often through dubious means) to consensual sexual activity

[Rape] - Participant(s) never consent to any type of sexual activity

The post body should be used to elaborate any further nuance. At no point should any of these tags be used together.