Mawilliams
The term originates from a historically significant man: William Rufus, who was king of england from 1056-1100 who was noted as cruel, selfish, self-indulgent and unjust. He died a mysterious death; leaving speculation that karma strikes those who are selfish.

The term 'Mawilliams' then came about, to describe someone who doesn't share with others, while generally being known as someone who always 'takes'.

Classically this is associated with the sharing of food, however the term can also be used to describe someone who doesn't share money, drugs or transport.
I can't believe you won't give me some crisps, your such a mawilliams!