An amalgamation of the words hectic and dirty. The expression originates from Morden, South London. Both words have the same connotation; an expression of amazement.
The words can also be reversed i.e.: "Dirty Hectics" or bastardized i.e.: "Rectic Flirties."
"That shit was hectic dirties!"
"Rahtid Koop that was some frederick flirties"