3) Pulling on Dumbledore's beard is not a good idea
The Headmaster had a twinkle in his eyes as he surveyed his students. The twins were giggling about something, having previously being engaged in truth or dare. A second year was looking nervous.
Dumbledore smiled, the results of this would undoubtable be amusing.
The student walked past him, and when he was near the silver beard, he tugged on it then ran away.
Dumbledore froze in shock. He was Albus Dumbledore, headmaster of the most prestigious wizarding school in Europe. How dare someone pull on his beard?! It was his pride and joy, his most defining feature!
It was elegant, mysterious, magical!
By now most of the students had noticed the dumbfounded headmaster, and a light giggling had broken out. He fixed the offenders with Voldermort-destroying stares, and stormed off to introduce the Weasleys and their victim to the Forbidden Forest.
And thinking about it, Fluffy needed feeding.