Evil doesn't always mean "I stab babies", it's "I look out for #1, and that's me, regardless of what the fuck else is going on". You're basically a massive jerk or self-interested twat. Just direct your jerkiness outwards from the party, and do things that aren't going to get your party caught and sidetracked.
If you want to rob the village shoppe, you do it on the last day as the party is leaving, not when you first show up.
If you want to kill this NPC, wait until after the party has all the information they need out of them. Better yet, don't kill them in a way that the party notices; if it's the party's intention to let this bandit go, don't just shoot him in the ass as he walks away. Give him some poisoned provisions for the road so he drops dead long after he's out of sight.
When the party wants to help the poor midwife clear some goblins for the orphanage or whatever, ask for a reward up front. If the party balks, extort money FROM THEM for your assistance in advance, or take a larger than equal share of whatever gold is found in a quest ("it was 50gp just to get me in the door, on top of my share of what we find"). Whenever reward is offered, insist on more. When you bring the town mayor's killers to justice, keep his wedding ring; the widow should sleep well enough knowing that her husband's killers are as dead as him.
But since you're a cartoon villain, just kill everyone in absurd and over-the-top ways while gloating and big-upping yourself in a melodramatic way. Have a speech and bad 90s cartoon one-liners prepared.
If the party is OK with killing these goblins, insist on gaining the goblins' trust instead. Then kill them.
Don't be discriminating when it comes to throwing fire around. Don't hit your party, obviously, but also don't give a fuck if you burn down a building.
"Overkill" only seems cruel if it's slow.