Person A now waddles backwards and sticks his boner into Person B's ass/cunt (cannot be mouth). Person A does an abbreviated squatting motion so as to fuck Person B, but all the while Person A is keep his legs closed and his balls up front.
Just prior to climax Person A will point to Person C and scream 'Bloody Mary'! It is at this time that Person C, who has been an innocent bystander til this point, takes aim at Person A's awkwardly exposed balls with a paddle or baseball bat.
Only moments before Person A blows his load, Person C will strike Person A in the balls so that upon busting, Person A will blow a bloody cumshot into Person B's ass/cunt. Thus completing the 'Bloody Mary'.
Lawrence: "Oh, it's no big deal. Me, Rachel, and Rob had Bloody Mary Sex last night. And I'll tell ya what, Rachel can really swing a baseball bat hard!"