I really liked your Norway theory! However, I have a question. Why does he sometimes smack Denmark? Like in the episode where Iceland does a DNA test and Norway grabs his tie, or in the school club episode when he tells the Axis to “Just flat smack him.” Is this just his way of showing affection, or is there something else behind it?

Thank you! All right, so I believe you’re talking about the second part of the Hetalia Academy strips. 

Your answer can be found in Norway’s character note from Volume 4. The wording is slightly different from the dub (which isn’t ever canon), but it conveys the same message.

“This young man’s mysterious aura makes it seem like a troll is standing behind him. His hobby is to gently poke at Denmark.”

Like you said, it’s just affection, even in the form of verbal quips. Note the word gently, as if to tease. There really isn’t any deeper meaning behind it.