Does Lee Sedol have a nickname? I've not heard any used for him in anything I've read on him including his Sensei's page and a search here. Seems improbable that a go superstar like Sedol would not have had a nickname stick by this point, so I'm assuming I've just not run across it yet?
The cheerful smile (seen here) shows up in many of the photo's of him, and he does seem to have a rather sunny disposition generally. Something coupling this and his chaotic playing style would probably be a perfect fit!

Where've you been? Zatoichi could slice the board in half, put it back together again and rearrange the position so fast that no-one even knew he'd drawn his sword - and he was blind. ~ John Fairbairn