Just assume (heh, heh) that the technology has reached the stage where we are collecting living human beings to be sent to Mars for the rest of their lives to do whatever it takes to start a civilization there. 100 folks in a reverse Noah’s Ark scenario.
Who HAS to be on that ride?
Explain your choice(s) if you must
Me! Me! I want to go!
Australians. Just ship 'em all to Mars.
Gingrich.
The entire starring cast of The Expendables must be included. 'Cause when the shit goes down, there’s nothing they haven’t collectively seen before.
Depends. Will there be hookers and blow?
Most of the batch I’m thinking of will be taking their own! 
Assuming the OP is serious, the size of the crew is quite important.
100 is remarkably large for an expedition, but too small for a colony.
But, given the constraints, I would make certain that there was a healthy gender mix of various professions ranging from biologists/medics to physicists and chemists with those pesky administrative types tossed in there somewhere. I would suggest that most people should be cross-trained in as many disciplines as possible.
Of course, the focus of the mission should be well-defined.
What does the OP hope to accomplish with this mythical mission to Mars?
This was not to be taken too seriously! 
The main objective would be to get them off of Planet Earth without resorting to outright murder.
Oh, now I understand. You are asking for a set of people that you wish to EXILE to Mars, right?
May I suggest Newt Gingrich?
He can be the Captain of the USS Useless.
That’s the ticket!
Glenn Beck
Rush Limbaugh
Everybody that threw a head covering into the Republican Primary ring
75% of the “stars” of Reality TV
A colony on Mars? Nah. Mars ain’t the kind of place to raise your kids, in fact it’s cold as hell.
Dick Cheney and his boy wonder put in stasis aboard the Botany Bay.
Libertarians. They’ll love all the freedom.
Damn, I don’t know if I can whittle the list down to just 100 people.
Let’s see…Rachel from Card Services deserves a slot, along with whoever hired her. In fact, let’s send EVERYONE who owns or has shares in a telemarketing business over there. If there’s still room on the ship, then I suggest that we start adding spammers, with the most prolific ones getting the highest priority.
Still got room? Newt Gingrich. Andrew Wakefield (the ex doc who started the antivaxxers) and every celeb who swallowed his nonsense.
I’m thinking that we’re gonna need more ships.
I understand rocket men like it.
And all this science I don’t understand.
It’s just my job five days a week.
With a nod to Jaws that’s the best line in the thread! 
Westboro Baptist Church. Somebody has to keep the gays out.
Oprah. She can keep morale up.
Glenn Beck. We’ll need someone to mine for gold.
Rush Limbaugh. He’s full of hot air. The colonists need lots of air.
Nancy Grace. Think about the children!!!
The cast from Glee. Everybody likes music.
Any actor who has appeared in a movie based on a comic book, & the directors of same. Let’s face it, the crew is doomed unless there’s a handsome hero there to pull them out at the last minute.
I say we send all the middle managers, security guards, public relations execs, telephone sanitizers and the lot, let the Enormous Mutant Star-Goat eat 'em all