The general feeling of despair and/or lack of motor coordination associated with the morning after a person has used ecstasy (MDMA). An ecstasy 'hangover', if you will.
"Fuck, you look skaggy. How many yokes did you take last night?"
"Man, those buzzers last night were shite. I'm so on the skag this morning.
"I'm so skaggy right now it's ridiculous. Seriously, just kill me. Savage buzz last night, though."