He tried not to laugh as he saw the merman crossing his arms over his chest, sternly frowning like an unhappy parent. The way he looked felt so human and way too funny for Keith's own good, so he began to chew on his lower lip making a silent oath to never let a single laugh escape his mouth at the sight. The wind swept against his hair as he sat up, watching as the other moved up a bit more up the deck, his entire chest now exposed to him, and with a small flip in his own chest he wondered what he was going to do. A part of him blared its alarms again, hoping he wouldn't get splashed or dragged into the water, and his eyes began to showcase slight worry before he felt the hand around his foot and felt the fingers against his toes. Immediately, the sensation of being tickled ran straight to his mind, and his teeth bit deeper into his lips.

"What are you doing?" he asked, a slight croak sounding in his voice as he tried his hardest not to laugh while also trying to stay still, completely not fazed and even challenging the other to do his worst. "I'm still not leaving!" he attempted to act like he was annoyed with the merman, trying to pull his foot out of his hold before he let out an uncalled for squeal among his thrashing, and his eyes widened at the creature like he hoped he hadn't heard that sound before he exploded in fits of laughter. At first, they were small, short giggles, then they escalated into full-blown chuckles, exactly like when the other man mispronounced his name. "Fuck, stop tickling me!" He covered his mouth, trying to pull his foot out of his grasp. It was a burning sensation to be tickled, a giggly kind of torture, and he was laughing so hard he was barely breathing. His voice echoed through the night, the way he snorted and wheezed like he heard the best joke of his life. 

"Mercy!" He said with a grin between laughs, holding his hands up in surrender and pleading with the merman to let him go. The part of him not laughing was wondering how Shiro knew to do that trick. Did he try it with another human before? Better yet, was Shiro ticklish on his tail too? He made a mental note to take his revenge later when the opportunity presented itself, but he realized he still wanted to say around for longer. Sleep wasn't such a good activity for Keith, since all it did was bring bad memories and restless nights, so he tried to convince him to stay. Just a while longer. "A little longer? Please?" He acted like there was a watch on his wrist that he pointed at, then made his best impression of puppy eyes, which wouldn't have come easily if he were sober. He even sat on his stomach cheeks in his hands, approaching the other so he could express his desire to stay with him more.