A heroin or crack / meth addict who only buys drugs on the day they receive their giro (benefits payment / welfare check). They differ from other drug addicts who will go to any lengths to get a daily fix as they tend to only use on their payday, so they are also known by their peers as 'King For A Day' as they usually blow 2 weeks money in one day and then end up skint til their next pay day.
That guy is just a "Giro Junkie" - he only scores on payday cos he hasnt got the balls to go out thieving to pay for a proper habit! Ha ha ha!!!