I have a few thoughts on this. First off, to answer your question, there is no way in hell I could ever do that, even at my skinniest point. I am and always will be too fat for that!
Secondly, if I could do that, I'm not sure I would, there is something odd about sucking your own weiner. HOWEVER, one could argue that there is no difference between whacking off with your hand, and sucking your own dick. Think about it like this: If you were to suck another man's penis, or jerk it off with your hand, you are probably gay (or in prison, haha). BUT, most every male jerks himself off (a lot), so you could argue that you're gay for that. They are both forms of masturbation, one form is just more... "intimate"... than the other. Just my 2 cents.