Thanks to Comme des Garcobs, the answer posed in the question will always be "yes". Yes, your butt DOES look kinda big in that dress, now you come to mention it! And so does you hips, toso, and... well, just everything, really.
That's the whole point, though: this dress is part of a whole range of "oversized" items from Comme des Garcons, and they're designed to make everything look that little bit - or, OK, that BIG bit - larger than life. We don't know: we guess you could say it's a refreshing change from all of the clothes designed to make us look smaller and thinner? And at least with these, you definitely won't have to worry about undoing your top button after dinner..
Just in case you're wondering if this idea looks better on:
We'll just let you be the judge of that.