From the Irish colloquialisms 'Sack' meaning scrotum and 'Mickey' meaning penis, SackMickey refers to a gentleman who has a bigger sack than mickey because of his tiny penis. This usually gives the appearance of a baby carrot resting on a large pair of wrinkly red kiwis.
Paddy: "I saw John's flute last night at the gym.
Sean: "Oh yeah? How was that?
Paddy: "Not great, full SackMickey on him"
Sean: "Jaysus, poor John"
Similar to "brown bagger", but the whole body, not just the face needs bagged or "cinch sacked." May even pertain to someone's overall rotten personality, appearance and general place in the world.