Hey, get them interested.
I would mention that the rumba is the dance of love, seduction, and using the audience as your partner, show interest then quickly turning away knowing that HE is watching. If you are comfortable, show the walk or have a visual.
Then mention that the tango is the dance of passion. You can mention the quick movements, the mastery of the man as the woman hugs his hip.
You might want to talk to the teacher first so he doesn't fear that the talk will be Xrated. Ask if video equipment or an overhead is available. Overhead transparencies are available at office supply stores if your teacher doesn't give you a few free.
This can lead into a talk on the five smooth and the five latin dances, how each arose, each unique's history and of course references to movies.
Dancing is on TV now so give them the characteristics so they know what to look for and an incentive to try. Fun, not dry facts.