No True Scotsman
The Fallacy
Changing the rules of a group just to leave someone out because they did something you don't like.
Why it's wrong
When someone in your group does something silly, instead of admitting it, you just say 'Well, they aren't a REAL member of our group then.'
Example
Real kids don't like broccoli! Wait, Tommy likes broccoli? Well, Tommy isn't a REAL kid then.
What the Fallacy?! (ELI5 Edition)