I love throwing out occasional Spanish comments to my students. It's hilarious to see the reactions.
On a rainy day, when we can't go outside and they're a little whiny about it, I might say, "Lo siento mucho."
monolingual students will look at the Hispanic students and whisper/mutter, "What'd she say?"
Hispanic students will have a sheepish smile. LOVING that they can understand when their friends can't. (Especially since sometimes it's the other way around!)
a couple of girls will get a really confused look on their faces like, "Did I miss something? What were those words?"