1. Seamus is NOT after me Lucky Charms
Harry was sitting quietly at the breakfast table, nothing amiss, nothing special going on, just eating a bowl of his favorite cereal, when a certain Irishman stepped into the Great Hall. Harry became antsy, fidgeting in his seat, trying to keep Seamus in his view for as long as possible. He knew he probably looked stupid but he couldn't seem to care right now.
He was trying to protect the most important thing to him right now. What it was, he would not mention it to anyone, but it was extremely important. He ignored the stares that Hermione was giving him in favor of making Seamus sit directly in front of him.
The clueless said nothing about this, only giving Harry a small look of 'WTF' before reaching toward Harry for something that was on the table.
Suddenly Harry was up in a flash, scattering things all about. He glared at Seamus and started to scream incoherent things at the boy, who was sadly, cowering in fear.
The rest of the people in the Hall stared, and wondered what was going to happen next. They were sitting on the edge of their seats. After all, it wasn't everyday that you saw the great Harry Potter freak out. Well, it was, but it almost never was on one of his housemates, the exception being his friends.
Hermione knew nothing of what was going on and tried to force Harry back. He was practically crawling over the table, and literally growling, to get to the Irishman.
"HARRY! What is the matter with you!"
Harry said nothing, opting instead to grab the box of cereal in front of him screaming the entire time.
"SHEAMUS IS AFTER ME LUCKY CHARMS!"
He even had an Irish accent to make it better.
The people in the Hall just stared before going back to their breakfast acting as if nothing had happened.
Half an hour later, in class Harry came in ten minutes late holding the same box of cereal and muttering to himself, "Seamus is not after me Lucky Charms. Seamus is not after me Lucky Charms. Seamus is not after me Lucky Charms."
Nobody said anything.
Common Courtesy was to never mention it again, and that was exactly what was going to happen.
Or wasn't. Your pick.
Done.