I try not to correct people unless they are my closer friends and most of them know about beer now because of me. We were all there once and it is hard not to come off like a beer snob when talking to strangers.
The Guinness meal in a glass thing messes with me though. I just don't understand how a sane person can really think there are like 500 or whatever calories in such an easy drinking beverage.
I tried for a time to correct this by showing them the calories on my smart phone and tell them it is like drinking a bud heavy (that's what they lovingly call Budweiser here in St Louis). It's always a shock somehow and they say that they think the Guinness that they brew in Ireland is different then and that is like a meal in a glass. whatever...I have given up. I just have them try my actual heavy stout or IPA and watch their faces.
About a month ago, I was out with some friends and had someone in the group question my choice on ordering an IPA. He kind of did it loud enough that it was like calling me out in front of the group. He said, "I thought you were a beer guy, don't you brew?" I said I did. He asked why I was drinking a "pale beer" then. He of course had a Guinness in front of him and said that he figured that I would be drinking the same.
I told him that I was a fan of most beer styles and do enjoy Guinness, but wanted something a bit heavier. I chose these words on purpose because the little devil on my shoulder knew that it would set him off and he was already kind of being a jackass. He of course mentioned the meal in a glass and the color as proof that Guinness was the heaviest beer. I had him right where I wanted him.
I politely disagreed and told him that he could decide for himself and bought him one of what I was drinking, unfortunately for him, I was drinking a Stone Ruination...
The mingled look of horror and embarrassment that went over his face was well worth the price of a beer. He kept with it and tried to keep drinking it but in the end could not. He gave me the fact that it was a hard beer to drink but still said that it was just because it was a bad beer. He said that no one would drink that beer. We were at a craft beer lover bar so I pointed out how often the Stone beers were being poured.
I then told him since he didn't like bitter beers, he should try what my girlfriend was drinking, if he liked stouts, he would probably like it too. I guess I am the jackass at this point because she was drinking 2nd Shift Liquid Spiritual Delight. After that, he conceded that he didn't know as much as he thought but still blamed others for his faulty info.
Since then, he ha been trying a lot of beers though so that worked out alright. The only problem is, a well informed jackass is worse because he'll probably pull my trick on others who are less deserving.