Start masturbating in public. People will forget whatever your other problem is.

Are you a generously proportioned italian assumed to be a mobster, by any chance?

hugely depends on the social setting and maturity of the people involved.

Learn to stop giving a fuck.

Fake my death; start over elsewhere.

It doesn't sound like you don't care about your image/reputation.

What I do is, I blast Joan Jett's "Bad Reputation" at full volume and dance around until I feel better.

Keep living your life however you want to. If you lean in to it that can solidify said stereotype, if you lean away from it people can see the opportunity to bully you further with it. Grey rocking the stereotype with simple disinterested answers will lessen it's hold over you. Like the other person said, if you're assumed to be a mobster, saying things like "yeah people have been making that joke all my life now", "ohh original havne't heard that before", "sure, watch out or I'll get the boys onto you." Passively engage with it giving it as little energy as possible and people will usually match that. If someone thinks they're hit comedy gold with your stereotype ask if they'll ever have any new material or are they planning on using the same tired joke through your entire relationship?

Nothing to be done - that image is all in the minds of other people, and you don't control what they think.

Just do you, people will be who they are.

So what should one do when they have an image they don’t care for?

If one doesn't care, why bother?

Wear a funny hat.

People don't randomly assign you to a stereotype. They based it off of your appearance and actions.

If you want to be seen as someone else, you need to act like that instead.

You should focus on being true to yourself and let others think what they want.
Anyone's opinion of you, that isn't close enough to you to know if it's accurate, doesnt matter.

Get a new group?

hermit.