you were making Amormentor potions in class the potion that smells differently to everyone based on what they're attracted too. Professor Slughorn has you smell yours first

You: I can't smell anything over Mattheo and those cigarettes

Mattheo: your always blaming something on me, a miracle anyone can smell anything over that perfume of yours

Slughorn informs them both that they were the only ones that could smell those things meaning it was the potion. Both there faces go blank