A Full Counihan occurs when both sexual partners are drunk enough to vomit, not necessarily simultaneously, but both must vomit during the sexual act. Addtionally, the man, or if the partners are gay men, one of the men, but finish by jacking off on their sexual partner.
Jack pulled a Full Counihan on Jill last night. They were both bombed last night and having sex. Jill threw up on the bed, and then because of that so did Jack. Still, Jack wasn't finished so he jerked off on her.