What new invention should I invent to make a lot of money?

[Just another dude]

An anti-taser shirt.

Or a shirt that you can connect peripherals to so they can communicate on a common bus e.g. your mobile phone can talk to your hat which has a camera on it and uses facial recognition to determine if you've seen a person before. If you've previously registered that you don't like that person then your phone could automatically ring so you don't have to talk to them. Also that hat could live feed to twitter / facebook to update your status on who you just blanked and automatically block them.

Then stats could be generated on the city's most disliked person.

Or if you think all that's a stupid idea then just take an existing idea an do it better / cheaper.