The possibilities make the mind reel.

YouTube Comment Snob is a Firefox extension that filters out
undesirable comments from YouTube comment threads. You can choose to
have any of the following rules mark a comment for removal:

• More than # spelling mistakes: The number of mistakes is customizable, and the extension uses Firefox’s built-in spell checker.
• All capital letters
• No capital letters
• Doesn’t start with a capital letter
• Excessive punctuation (!!!! ????)
• Excessive capitalization
• Profanity