Okay, BOG, now everybody knows that you're not being honest with yourself on this matter. Here are some other examples for you:
It is impossible for the statements "one plus one equals two" and "one plus one does not equal two" to both be right at the same time and in the same respect.
It is impossible, by definition, to meet a married bachelor (so long as we mean the same thing by 'married' and 'bachelor').
These a priori things (and many others--such as the three-sided-octagon already mentioned) are things that are impossible.