The moment where after making a Heroic Sacrifice that simultaneously saves the world and rescues an innocent soul from Hell by killing himself to summon Satan to collect his soul, said sacrifice causes Constantine to start ascending to Heaven... and flip Satan off while doing so.
What about Lucifer reaching into Constantine's lungs and pulling the cancer out? That was pretty fucking special.
Lucifer demonstrates just why he is the boss of his domain by effortlessly dealing with Mammon.
John and Chas taking out a room full of demons by first blessing the water in the sprinkler system of the building, then setting it off with a lighter, than taking the survivors down with shotguns loaded with holy bullets.
"The name of that is pain. Get used to it."
From the series
In the Pilot the demon tells John he can't trap him because he could draw in the electricity from around them and John lacked the "Power of Intention". Cue the Power Grid being shut own and the magic circle being set on fire via light toss.