A golden ratio inequality for vertex degrees of graphs

Motivated by the study of the crossing number of graphs, it is shown that, for trees, the sum of the products of the degrees of the end-vertices of all edges has an upper bound in terms of the sum of all vertex degrees to the power of ${\varphi }^2$, where $\varphi$ is the golden ratio. The exponent ${\varphi }^2$ is best possible. This inequality is generalized for all graphs with bounded maximum average degree.