Jealousy
Ron practically steamed in the corner of the Gryffindor common room. His ears were bright red and the glower on his face could have matched that of the Basilisk. Everyone in Gryffindor could tell the subject of his disgruntlement: the sight of Harry Potter and Hermione Granger giggling and exchanging kisses. It was almost sickening how sweet they were, and Dean Thomas was entertaining half the house with a (fairly accurate) mime of the couple. Every exaggerated sigh, every mouthed "Oh Harry!" only made the Weasley grow more and more irritated.
It was the funniest thing the House of the Lions had seen for a long time.
The twins were even considering making t-shirts.