I wouldn't worry about 1 guy attacking 2 in this situation.
The problem is, you can't assume it's just one bad guy. Like with a gun, just because you don't see it, doesn't mean there isn't one--it's more than possible that the BG had friends in the immediate area ready to come out.
Lots of good info in this thread, especially the post about keeping your arms crossed with one hand on your chin. If you lean your head in while you do it, not only do you have both hands up, ready to defend, you've also got your head in perfect striking distance for a headbutt. Obviously, headbutting someone is never your first choice, but if your back's up against the wall and you dont have an escape route, a headbutt to the nose or chin followed up by a kick to the groin is very effective.
There's also a lot of talk about never letting yourself get in situations like these, but the honest truth is depending on where you live, work, or socialize, you just can't avoid them. Especially as a smoker, anywhere I go I'll inevitably end up outside, leaning on a building, smoking a cigarette--my back is literally against the wall (it's that or stand in the middle of the sidwalk, annoying everyone.) I get hit up for change or smokes all the time by new bums (the old-timers know I don't give out), but I've never had that particular situation escalate into an obvious interview. (Saying "don't have anything," "last one," or "nope" has always been enough to turn them away.)
Never go back on your word. If you tell a guy you don't have anything and he keeps asking, don't fish around in your pockets for show. You're telling him that he can manipulate you, you're showing him where you keep money, and you're momentarily disabling your most immediate defense. I usually just say "I told you, I don't have anything. Ask someone else."
I have had two hairy situations on my way home late at night, though. I don't have a car and Philly public transportation after midnight is sporadic at best, so most of the time it's just me and my Doc's. Smoking in those situations was actually a benefit--I get to keep my dominant hand up almost constantly without arousing their suspicion. Using a weapon is an absolute last resort for me, so I'll use my knowledge of the city to my advantage, walking towards police stations or popular cop hangouts (24 hour gas stations, convenience stores, drug corners, etc). Walking towards a drug corner may not sound like the smartest thing to do, but it's a viable option when you know there's a 98% chance there will be a squard car parked across from it. There were other things I could have tried, but in both situations the interviewer was obviously on crack--I couldn't count on them making rational decisions, so I played it by ear and pretended to be friendly until I could ditch them, or they gave up and went to find another mark. Regardless of anyone else's opinion, I made it home safe and sound both times, and never had to be obviously aggressive.
