Does this one-line proof qualify?

$$1={\rm Pf}\,\Omega={\rm Pf}\, (M^T \Omega M) = ({\rm Det}\,M)\,({\rm Pf}\,\Omega)={\rm Det}\,M,$$
where I have used the defining property $M^T \Omega M=\Omega$ with $\Omega={{0\;\;I}\choose{-I\;0}}$.