His self deprecation, his voice, his swagger, his persona.
He should let his hair grow a bit. I just watched the Walk On performance from 2001 (9/11 Heroes thing) and he looked GOOD. No shades, a little longer hair, somewhat clean shaven. I'm a guy and I thought he looked good! LOL
IMHO, I think Bono looked best during AB/Zooropa and during ATYCLB.