A weak
individual who is regularly abused by others.
Example:
1) Ned
will never get anywhere until he stops being such a doormat.
2) I wish people would stop treating my brother
like a doormat.
Etymology:
A
'doormat' is where people wipe their feet before entering a house, so
someone who is called a 'doormat' is someone who gets 'stepped on' or
abused by other people.