It's not gonna be King. The guy who took over of the situation like a leader, and shitting on Queen for his incompetence, will be out of character if he suddenly goes having fun with Black Maria and her prostitutes groups.
It's Fukujurou. The poor old man got shocked seeing his Master got murdered right in front of him, so he went to red district to relieve some stress. Either him, or Who's Who, who's at least already hinted to have womanizer side, when he was seen having fun with his 2 catgirl crewmates.
"but but Katakuri has Merienda"
Not same situation, Katakuri was viewed as the perfect one among his brothers, so his Merienda scene was supposed to show his real side, the secret hidden literally behind his scarf. While King wasn't seen as perfect one, as Queen always shittalked him, and some of F6 don't really respect him as much as Kuri's siblings respects Kuri.