Perhaps lost in design education is the art of "the sell." Often the result of art school critiques is an excellent exercise in rationalization. It's like a design jujitsu match, the result simply being how to defend yourself from the onslaught of other people's bad taste. What really needs to be taught is how to go on offense. Know what you need to say before they get the time to really ruminate in their own thoughts for too long. The class could be named "Don Draper 101" after the great Mad Men character.
An Honest Salesman
Designers try not to imagine themselves as salespeople, all the while throwing around sales lingo and killing themselves to sell their services. So first, we need to get beyond the idea of selling your self and your work being like selling used cars.
The best way to be honest is to weigh rationale over rationalization. The two are quite similar – so similar they are often conflated. But, rationale comes before the work, and rationalization comes afterward. Creative briefs are used to do this on the grand scale, however, we designers need to additionally be conscious of the choices we make and why we make them. Know why you used an quarter inch grid, or why you couldn't reverse the logo, or why the logo shouldn't be bigger (good luck with that by the way). Going into a client meeting armed with that kind of information makes for a much easier meeting, and results in a lot less backpedaling.
No Silver Bullet
Unfortunately, we all know that design is a bit of an intuitive enterprise. So try as you might, as hard as you think, as much as you'd like, sometimes you do something just because you think it looks cool. Well, this is where rationalization comes in handy. You know, "It's red because it represents the fire and drive your company has," or, "it's blue because you are such cold, calculating sons-of-bitches." This is known also as bullshitting. These sorts of things are much more articulately described by Michael Beirut.
But note, rationalization isn't bad. It's just not as strong as rationale. Rationale allows you to articulate the truth about your work, and why it works. It allows you to say you've done your job. it allows you to walk away if an impasse forms. The rationale is what designers do. The rest is fun...and kind of bullshit.