My brother ride the BMX bike. He love this, and is very good with this. So my brother when he see the girl deliver the mail always go do the bike trick in the street when she is walking. He think she is "hot" so he want her to see him do tricks on the bike because he like her, and want to be the peacock. Then the letter from the post office came to my house to say my brother is "obstructing" the mail service, "this is federal offense". So the girl complain, but really my brother like her and want to have her attention. He really is not trying to obstruct the mail. This was the warning to him, but no charge to him. My question is how is the bike trick obstruction of the mail?