Don't use listings commands in \item[..] context:
```
% pandoc -t latex
`--foo` **BAR**

:   Enables the foo feature with **BAR** as its flavour.
^D
\begin{description}
\item[\texttt{-\/-foo} \textbf{BAR}]
Enables the foo feature with \textbf{BAR} as its flavour.
\end{description}
```
