Portmanteau of "leave" and "retard". Someone of British origin who voted leave in the referendum on membership of the European Union. Typically describes someone gullible, uneducated and incapable of acting in their own best interest.
These leavetards just voted to piss away all of their jobs and money, how stupid can you get!
A person who always uses "leet speak" in their writing not because they think it makes them look cool but rather because it's the only way they know how to communicate. Lacking the most basic knowledge of Elementary school English they apparently learned this strange sort of strange phonetic based pseudo-language entirely from each other instead to make up for having so much as a 3rd grade education.