I understand your need to want to examine him up close, but since you just got him, I think the best thing you can do to start out here is to leave him alone fora couple weeks - let him get familiar with his new surroundings, have a couple meals, and then see how he does. It could be that he is simply stressed right now.

And yes, 2 rows of teeth... 

What Sonja said. Just let him be for a while. Once he gets acclimated he will get better. Right now the more you try to handle him the more you're going to get bit.

Going to echo the sentiments of Sonja and George - in my experience, when you're taking in an adult snake, you have to give it a bit of breathing room before you attempt to handle it or feed it. Chances are the snake was set in its ways in its previous home (5 years is a relatively good amount of time to be accustomed to the same thing). Do you know anything about its previous owner?

As far as I'm concerned, new-snake-adjustment goes as follows:

1.) soak (particularly if it's picked up from a show, namely because being in deli cups, stressed out for an extended period of time leads to dehydration - this may not be the case with you)

2.) introduce to the new habitat (once you've made sure that you've cycled the temperatures a few times and that they're stable and correct for the species - having a big temperature variance between homes can definitely create some behavior modifications, even if they're temporary)

3.) leave it alone for a while - at least a few days, but I prefer to wait closer to a week. Observing from the outside will give you a chance to note any potential ailments (URI, mites, nose-rubbing, etc), and to allow them to get used to your particular day/night schedule (nobody's are identical). Extenuating circumstances can occur where you have to attempt to feed earlier than this, but more often than not, they're fine.

4.) attempt to feed - be sure you know whether or not the BRB was eating live or F/T in its previous domecile (it can make all the difference)

5.) once you've had a successful feeding schedule set into place for a few weeks, allowed them time to adjust to their new habitat and its inherent temperature/humidity gradients, ruled out any outstanding ailments, then you can start messing with him - but do so carefully, and for small amounts of time at increasing intervals. if they associated being handled with being out for a long time and getting pissed off, your scheme will start to work against you. :-)

This is my general policy for adult snakes. I usually expedite the process for babies/hatchlings, but it doesn't surprise me that a 5 year old BRB of all things is a little stubborn. :-)   Good luck! And remember, even if the bite isn't particularly earth-shattering or painful, you're getting bitten because the snake is trying to send you a message, and if you continue to not get the message, they will continue to try to send it and maintain a certain level of stress about it.

Hope this helps! Again, this isn't any set-in-stone policy, it's just how I handle any adult snakes I take in, and it's worked marvelously for me thus far (I still have YET to be bitten! - perhaps that's just dumb luck)

Oh, and FYI, some BRB's are just jerks. They have to be, they're just so fancy! ;-)