EPT"In the back of my mind was this voice telling me about how rude I was, and how I should bail, blah blah blah. But I was in the middle of the moment, and I was just going with it."
Another way to put it would be "but I decided to say fuck it and be rude anyways". Sure the guy let you do it and it ended up being no big deal, but did he really want to do it? and if it was actually expensive your bite depending on how big it is could have been a dollars worth or more. One symptom of rude people is they really only consider their perspective for example: "well if I was in his position and someone like me came up with good intentions and asked this way I'd be fine with it". When he said "are you fucking serious" would have been a good time to apologize and just ask how the burger is as opposed to continuing to ask for a bite, you put him in awkward spot and yeah pretty much forced him to share his burger even though he likely didn't want to because his GF found it funny. He either has to do something he doesn't really want to do or look like a humorless fatty jerk.
Maybe I'm analyzing too much too but it seems you were more worried about the guy spitting in your face (you getting a personal inconvenience) rather then you coming off as an overly imposing person.(even though that's what you were doing).
