When someone is always slow, sluggish and tardy. In a crisis they still maneuver like they are wearing medieval plate armor, and generally have the agility of a tractor with a missing wheel.
Don: 'Why the HELL haven't we finished this production yet?!'
Gibbo: 'Operation Slow-mo over there is doing his tortoise impression again.'
Don: 'Bloody hell, he's not even morbidly obese the guy's just in a permanent daze. His mum must be a starfish and his dad a freakin statue! You're fired, land porpoise.'
Land porpoise: 'It just looks like I'm going slow!'
Gibbo: 'WTG Captain Obvious. It's looks like that to everyone else too.'