This person is my younger brother, Jeff. (I also have a youngest brother, Steve. We're all about two years apart, so Jeff is two years younger than me, and Steve is two years younger than Jeff.)
For example, I mentioned to him today that I'd been reading up on bartending, and would likely be doing that as a part time job for the next few months. During the course of the discussion, I'm not exactly sure how it came up, I mentioned something about the size of a shot, and how it was 1 and 1/2 ounces. He jumped all over me claiming that a shot was 1 and 1/4 ounces, that he knows for sure, and that his friend is a bartender, etc, etc.
I calmly mentioned that I'd been doing a lot of reading in the past few days, both from websites, and a handful of books I looked over at B&N, and that pretty much all of them listed a standard shot as being 1 and 1/2 ounces. He said I was wasting my time, the only site I needed was webtender.com. I noted that I'd been to webtender.com, read most of the articles there, and was pretty sure they listed a shot as 1 and 1/2 ounces. He went to get something to drink, and I went in to pull up webtender.com.
Sure enough, webtender.com listed a shot as 1 and 1/2 ounces. When I told Jeff that, he looked at me for a second, then said, "Well, they're wrong." He then walked out the door and left.
I know a lot of people have trouble with siblings, but I don't know that I've ever met someone as "difficult" as Jeff is. He will argue anything and everything anyone ever says, no matter what it is, he always has to be right, and he's perfectly willing to throw a temper tantrum if needed, despite being 22 years old.
Oh, well. At least I don't have to deal with him nearly as much as I used to.