Dirk doesn’t understand why UU likes all that weird shit like holding hands. Because to Dirk that is just normal average day stuff. But since Dirk lives alone he has never really hugged or held anyone’s hand, not even his ‘Bro Dave’.
So, when the two are on pesterchum together sometimes Dirk likes to tease UU about how he is gonna hold his hand, and hug him all night. It makes UU turn into a giant blushing skull. However, Dirk just likes to tease UU because its all funny to him.