The screenwriter behind The Fighter co-wrote Joker with Phillips, so I doubt it'll be awful.
I need more context around this particular scene before fully judging it, since it's something the Joker would absolutely do. A fictional mass murdering clown does horrible things, go fuckin' figure.
Also, there's nothing wrong with thinking the Joker is "cool", since he is after all NOT REAL. Tons of people root for Ledger's Joker in The Dark Knight. General consensus is that he's a great supervillain, but anyone with two functioning brains cells understands that he's a terrible human being (if you even want to call him that).