Prevent from the user to submit any 'not legal' input, in client side

Prevent from the user to submit any 'not legal' input, using client side validation. What if you have a rule that is for all inputs in the page, or in the site? for example, you want to prevent the user to submit any input that contains 'fuc*' , 'shi*' or what ever words that are not 'legal' for you, or input that is not valid for the ASP.NET such '<'or '/>' ?