This is probably Catullus's most famous poem. Just two lines. It's an elegiac couplet - a hexameter followed by a pentameter. I've tried to preserve the metre in the translation.
Odi et amo: quare id faciam, fortasse requiris.
Nescio, sed fieri sentio et excrucior.
I feel both love and hate; and if you should ask me the reason
I've no idea, but it's true, and it's a bitch of a thing.