"Gimme a crisp ya bollix!"
"Feck off ya scab."
"Ahh, go on..."
"No. Go and buy your own crisps."
"Scabby bastard ya."

Sound familiar? No? Growing up in Ireland, "scab" was a phrase often used to describe the process of obtaining goods or services from a fellow school chum or sibling for free. For example, if I pulled out a packet of Tayto Cheese & Onion crisps (like, Potato Chips, or whatEVER) in the playground at lunchtime, a fellow classmate may ask me if he can have a crisp. By doing this, he would be "scabbing" off me. I would then be in a position to either give him a crisp or call him a "scab" or a "scabby bastard". After some time, the person with the crisps would usually relent and hand over some of the delicious, salty goodness.

However, and this is where even I get confused, if the person with the crisps refused to hand over any of their snack, then the scab would be in a position to take the hump and call the person with the crisps a "scabby bastard" because he wouldn't share. "You're such a scab" or "ya scabby gipsy, give us a crisp, hey" would then be an appropriate response. The exchange would usually end there, or, if things got a little heated, there could be a claim(fight/scrap/rucus).

Sounds confusing, but it made sense at the time.

Having just confirmed with my nephew, the Scab System is still in place in the playgrounds of Ireland.

BlakJak says re scab: In Australia, we too use the word scab in this way. Substitute the Irish idiomatic phrases for Australian idiomatic phrases, and it's totally the same thing.