Offensive term used to describe a member of the travelling community. Pikey's (or Knacker's as we call them in Ireland) are a race of their own, they are genetically different from the rest of us. The average pikey is illiterate, ignorant and uneducated, they also show a complete lack of desire to succeed in life.
Inbreeding is commonly accepted as the norm as they do want to mix with the settled people (also because a settled person would rather die than touch one of them) therefore each generation is more messed up than the one before, for example,
father and mother have one son and one daughter, 15 years later the son and daughter get it on and have one son and one daughter and 15 years later...... and so on.
Basically they are misfit scum that should be exterminated, Where's Hitler when you need him!?!?!?
PIKEY: Howaya, can i have a pint of guinness
BARMAN: Get the fuck out you dirty pikey.