2009 Nyjer Morgan. He was electric. He was fun. He made the on field product significantly more entertaining.
Oddly enough, 2010 Nyjer Morgan would be my 2nd least favorite short time player. Pretty sure that second year it was a completely different person in the same body - the change in attitude and behavior was so dramatic and not in a good way. Paps get the 'least favorite Nat, ever' award.