Knock knock. Who's there? Europe. Europe who? (You're a poo.)
Europe Who
Explanation
Explain Bear
Listen here, lil' buddy. This joke relies on how "Europe" sounds like "You're a poo." Now, I know yer probably used to eatin' yer own waste, but most folks don't appreciate bein' called names, especially when it's somethin' as unflatterin' as "poo." Get it? You probably still don't.