Very often, when we're just starting to have sex, Alan and I will smile at each other. Or flat out laugh. Later on stuff will get serious, we'll wear our tight-set determined faces or our pleasure/pain grimaces or wide-eyed gasps, but in the beginning we can realize how silly the whole thing is.
There's some strange mix of joy and embarrassment and hilarity that washes over us. "Goddamn, I've got part of another person's body inside me and we're ass-naked and making ridiculous noises... and I love it."
What can you do but smile?