"No relation."

Fans of Tiny Toons might recall the tagline Babs and Buster Bunny used when introducing themselves. Despite their shared last name and physical resemblance to each other as well as Bugs Bunny, there was no familial connection and they were always particular to add “no relation”. After all, there was an obvious attraction between the two, so they had to be clear nothing untoward was occurring. Let's examine some other characters who aren't related:

1) Dr. Bob Kelso of Scrubs and Michael Kelso of That ‘70s Show
Despite frequent references to his son, it's not likely that Dr. Kelso's son is in fact Kelso. For one thing, Dr. Kelso often alludes to his son being gay, while Kelso is a notorious ladies man. For another, Kelso has a brother while Dr. Kelso has never mentioned any other children. Finally, Scrubs is set in the present day while That ‘70s Show is, not surprisingly, set in the ‘70s. A teen in the ‘70s would be in his 40s by now, too old to be the doctor's son and too young to be the doctor himself. Whether or not they might be cousins is a mystery for another day....

2) Alex P. Keaton of Family Ties and Michael Keaton
Believe it or not, this actually confused me for a time when I was a kid since the man who played Alex Keaton's dad, Michael Gross, shared a first name with the actor. Eventually I would realize Michael Keaton was not Alex P. Keaton's father, and that neither were related to Buster Keaton.

3) Principal Seymour Skinner of The Simpsons and Assistant Director Walter Skinner of The X-files.
While both are authority figures in a school and the FBI respectively, the former is animated and thus can't be family...can he?

4) Buffy Summers of Buffy the Vampire Slayer and Scott & Alex Summers of The X-men.
While the character Buffy started out as an only child and later gained a younger sister through mystical means, no reference has ever been made to brothers. Scott and Alex were mutants, orphaned at a young age. Alex was raised by a foster family while Scott grew up in an orphanage. Neither had a sister, although they may have another brother besides each other.

5) Dave Rhodes and Jim Rhodes, A.K.A. War Machine.
One blogs while the other fights crime in a suit of armor. Neither have ever been seen in the same place at the same time. Granted, the complexions don't match, but it could all be part of an elaborate ruse. He is, after all, an actor...

6) Mike Novick of 24 and Jerry Novick.
I'm actually not sure of this one. I've never met J-No's brother and, for all I know, he very well could be a fictitious White House Chief of Staff.