R.E.S.P.E.C.T. tell you what it means zu mich

I was strolling through my local shopping mall yesterday when a young Credit-Card salesman buttonholed the Dad with a young daughter in from of me.
'excuse me, Sir...' he began till he got the brush-off. Then he turned to try his luck on me.
'Hey, buddy...' he started, but my only interest in credit cards at the moment is which scissors are best at cutting them up!

But why did the other guy rate a 'Sir', yet he felt he could address me as 'Buddy'? Do I LOOK like his buddy?

But it made me think of something that happened in Germany, not once, but twice.
Both at Hamburg and in Hannover, while being involved in festivals, children came to me and said 'Du bist ein Clown!' (you are a clown) Yes, I admit I had some face-paint on, and a funny hat, and yes I was acting up at the time, but the point is, to correctly address an adult in German, especially one they don't really know, shouldn't they have gone with the more formal 'Sie sind ein Clown...' ?

I get no respect...