$\DeclareMathOperator{\dist}{dist}$ $\newcommand{\bR}{\mathbb{R}}$ $\newcommand{\pa}{\partial}$ Suppose that $N=2$ and
$\Omega$ is is the unit disk.   Choose 
$$
u= -1+ar^4+br^5\in C^2(\overline{\Omega}).
$$
Then $u=0$ along $\pa \Omega$ implies $a+b=1$.  Next
$$
\Delta u=\frac{1}{r}\pa_r\big(\; r \pa_r u\;\big)= \frac{1}{r}\pa_r(4ar^4+4br^5)=16ar^2+25br^3.
$$
The equality $\Delta u=0$ along $\pa \Omega$ implies $16a+25b=0$. Since $a=1-b$ we deduce
$$ 16-16b+25b=0\implies b=-\frac{16}{9},\;\;a=\frac{25}{9}. $$

Note that
$$\pa_r u=\frac{1}{9}\big(\; 100 r^3-80 r^4\;\big). $$

Along the boundary we have $\pa_ru=\frac{20}{9}$ which implies  that

$$ u(x)\sim \frac{20}{9}\dist\big(x,\Omega\big)\;\;\mbox{near $\pa\Omega$}.
$$