1. A thoroughly unprincipled person; a scoundrel.
2. A foul-mouthed person.
3. The criminals and vagrants or vagabonds of a town or community, collectively.
4. A person of stained or low character, esp. one who uses scurrilous language, or treats others with foul abuse; a scoundrel; a rogue.
5. A vagrant; a bootblack; a gamin.
6. A guy who runs EQII.com
A man whose manners and sentiments are decidedly below those of his class deserves to be called a blackguard.