  Given an $n$-vertex digraph $D$ and a labeling $\sigma:V(D)\to [n]$, we say
that an arc $u\to v$ of $D$ is a descent of $\sigma$ if $\sigma(u)>\sigma(v)$.
Foata and Zeilberger introduced a generating function $A_D(t)$ for labelings of
$D$ weighted by descents, which simultaneously generalizes both Eulerian
polynomials and Mahonian polynomials. Motivated by work of Kalai, we look at
problems related to $-1$ evaluations of $A_D(t)$. In particular, we give a
combinatorial interpretation of $|A_D(-1)|$ in terms of "generalized
alternating permutations" whenever the underlying graph of $D$ is bipartite.
