The cartoon shows a group of men having a drink and playing dominoes in a rather seedy-looking pub. One of them, who has been reading about the gay marriage vote in his newspaper, has a faraway look in his eyes. One of his drinking companions tells him, "Don't raise your hopes, Norman. I've got a feeling that Brad Pitt is already spoken for."
We must assume that Norman is gay, and that he is dreaming about getting married. The joke is that Norman is not the sort of person Brad Pitt would be attracted to (even if he were gay).
1. To raise someone's hopes is to make someone expect something that they want even though you are not certain it will happen. • I don't want to raise her hopes about the promotion until I'm sure.
2. If something or someone is spoken for, it is already claimed or being kept for somebody.
• I'm afraid you can't sit there—those seats are spoken for.
• Liza is already spoken for (= she is already married or has a partner).