Some artists know, without a doubt, that they just don't posess that traditional rockstar look. In this case, the best thing to do is just embrace it. You can go completely oddball and paint yourself blue, as a nod to the Blue Man Group. You can sing in your best montone about complete nonsense, like John McCrea from Cake (best known for "The Distance, and a cover of Donna Summer's I Will Survive). You can go potty humor like the boys in Bloodhound Gang. Or you can mix your real musical talent with jokes, like Tenacious D or New Zealand's HBO duo Flight of the Conchords.
Many of these bands can really play and sing, but it's easier to make fun of yourself than have others make fun of you.
Tenacious D's singer/actor Jack Black has a high and low range most vocalists would envy, but he sillies up his performance...peppering in jokes about his bodily functions.
Flight of the Conchords recently released their debut full-length album, and using their jokey status allows them to explore every genre: Dancehall, Folk/Balladry, Faux French, even spaced-out Bowie. They escape the persecution regular muscians would receive for bouncing all over the musical map.
The moral? When in doubt, form a novelty band.
Listening: Tenacious D and the Pick of Destiny movie soundtrack
Quote: "You're so beautiful, you could be a part-time model"-Flight of the Conchords