  We establish complete characterizations of the notion of Li-Yorke chaos for
weighted composition operators on $C_0(X)$ spaces and on $L^p(\mu)$ spaces. As
a consequence, we obtain simple characterizations of the Li-Yorke chaotic
weighted shifts on $c_0$ and on $\ell^p$ ($1 \leq p < \infty$) that complement
previously known results. We also investigate the notion of Li-Yorke chaos for
weighted shifts on Fr\'echet sequence spaces. As applications, we obtain
characterizations of the Li-Yorke chaotic weighted shifts on K\"othe sequence
spaces depending only on the entries of the K\"othe matrix and the weights of
the shift.
