A bit of grease from pizza residue or lipstick doesn't do too much to eliminate soda bubbles, but if flattens the head on beer. Why?
The bubbles at the top of a newly-poured glass of soda and the bubbles at the top of a newly-poured glass of beer look pretty much the same - at first. Differences make themselves obvious fairly quickly. Soda bubbles lack fortitude. They fizz down to nothing quickly. Beer foam stays, even when it's not wanted, until something greasy hits it.
How does grease tear apart beer foam? The bubbles in that foam are not as simple as they appear. They are supported by proteins and carbohydrates that they dredge with them as they precipitated up out of the beer. These molecules provide structure and stability for the foam, but they're vulnerable. Grease lowers the surface tension of the foam, ripping the structures apart, freeing the gas inside them, and causing the head to collapse.
Darker beers have more carbohydrates, and so their foam is more stubborn. Some people use nose grease to cut the foam, but those people are disgusting. And they clearly live way too far away from french fries or pizzas, which will provide all the non-human grease anyone could want, and something to snack on between sips.
Image: Public Domain Images
[Via Chow Hound.]