You point out what appears to be a bright star in the sky and then let them take a look at what it really is. They can't believe that they're looking at another planet with rings and moons around it. The visual resolution isn't a whole lot different than the pictures of Saturn at the top of this thread.
Like so:
In Winter, I like to point at the Orion Nebulae, telling folks "See the belt of Orion? Those three stars next to each other, one, two, three? That second fuzzy one between the other two isn't a star. Now have a look at it through the telescope" and watch them gasp at what they're seeing.
On the chance you're in a location with no light pollution, you can point to the Andromeda galaxy (M31) without even using a telescope and they'll understand that it indeed is our nearby spiral galaxy neighbor... Then you show them in a telescope and they'll be hooked.
Even a cheapie $100 refractor beginner telescope from a toy store is WAY better than the telescopes Galileo used, and I've seen one that reportedly belonged to him myself.