We know that the Weak Maximum Principle assert that for an uniformly elliptic operator $L=a^{ij}(x)D_{ij}+b^i(x)D_i+c$, if $c\leq0$ and $Lu\geq0$ in a bounded domain $\Omega$, then $u$ attains on $\partial \Omega$ its non-negative maximum in $\Omega$.
I wonder whether there exists an exact example show that with the same condition, $u$ may attains its negative maximum in the interior of $\Omega$?