Can we take a closer look at this gif please?
Here, Hook is trying to make Emma jealous. We know this by his words. But let’s look at his body language. First, he kinda sorta grabs his crotch
*heavy breathing* tucks his thumbs into his belt buckle…but then he tucks his tongue in his cheek.
According to the Internet and affirmed by virtually any girl who has ever flirted with a guy and can recognize the signs, when a guy grabs his crotch or draws attention to his crotch by tucking his thumbs into his belt buckle, that is a universal way of saying “I’m interested in you, please notice how manly I am.” Even though we already knew Hook was interested in Emma, it’s worthwhile to note that in this scene, Hook is trying to get Emma to realize his physical appeal
as if she hadn’t already because really who could miss all THAT and say "Well if you won’t tap this, I can find someone else who will, because I’m SEXY AND I KNOW IT."
Have you ever heard the phrase “tongue-in-cheek”? The dictionary definition is “meant or expressed ironically or facetiously” - in other words “don’t take what I’m saying seriously.”
So even while Hook is trying to act like a player and swag like a player, Killian is saying “don’t take me seriously Emma, I love you forever!”
(not my gif)