He laughs, though there's a very, very obvious fond edge to it.

"Sure, but let's see how I feel about stepping in the water first before I try swimming. Or learning how to."

He knows it'll probably be fine, but Inigo knows how his brain works and how it randomly makes him freak out about things. He just wants to make sure to take baby steps with this so he doesn't look like a total idiot in front of his boyfriend while Yuki is trying to help him learn how to swim.