I don't knit a whole lot when I'm in public. I have nothing against it though. I knit in the car sometimes when the scenery is not compelling. You really have to consider the type of knitting. I don't try to knit something that needs concentration when I'm supposed to be listening to my husband talk ;-). I think the reason I don't knit a lot in public is that I have lots of time to knit at home and more social moments are rarer. People who have little time for knitting, I don't blame them for trying to squeeze it in whenever they can.
Someone said you should be able to knit anywhere you could read. If the knitting is simple I don't find a correlation there. People don't usually read and watch a movie at the same time, but this is very easy to do with simple knitting. I recently went to a series of health classes that lasted over 2 hours each. I didn't knit when a live speaker was talking and people were interacting, but during the long DVD lecture, I knit. Room darkened, I don't click when I knit and I was in the back of the room. It was simple knitting and I looked up when they were showing an important chart or graphic and off and on the rest of the time. I think many people can knit during lectures (well chosen knitting). Not bothering other people would be the big consideration, not if the knitter could do it.
I knit anywhere I can. I spend many days a month at doctors offices and I always have to have my knitting with me. I dont really carry a purse, but a large tote bag that has everything in the world in it. Knit mags, knit needles, yarn for more than one project, snacks, wallet etc. I knit at dinner when my companion is eating, I am always done at least 20 min before him, he is so slow and I would go insane if I didnt. I use to read before learning to knit, so I think he is use to it. I can carry on a conversation while knitting so I dont find anything wrong with it.
I knit in front of the tv, while on the phone sometimes, as my sister and I can have a 2 hour chat. If I wasnt always the driver but was fotunate enough to be the passenger then I would get even more knitting done. I go to a sewing group get together on thursdays afternoons and since I am not a hand quilter but a machine quilter, I bring my knitting. I have to say I have turned at least 6 people I know into knitters that werent when I met them, some thursdays no one is sewing and everyone is knitting or crocheting.