The act of a male and female letting there pubic hairs grow to the point roughness, in which they sixty nine each other while rubbing there faces in each others pubes. Poking and probably hurting one another (depending on how long they haven't washed and grown) giving the imagination of rubbing your face on a cactus for sexual pleasure.
Friend 1: "Hey man did you hear what joey did last night? Him and Diana totally Sea cactused each other"
Friend 2: "That's gross... did it feel good?"
Friend 1: "I don't know we should try it"
Friend 2: "I don't like the idea of doing The Sea Cactus"