Just look at him and say: "Jesus Christ man! What the hell is wrong with your peepers! I can't tell if you are coming or going, looking at me or something behind me, below me or to my right."
This is correct. I have strabismus in both eyes. One eye will always be looking at what I'm trying to look at, while the other eye will drift outward. It's not something I'm even aware that I have, and it's never been a handicap in any way. I'm near sighted in my right eye, and I'm far sighted in my left eye. I go without wearing eye glasses much of the time when I'm in my home. I just use my right eye for reading, and my left eye for watching TV. My brain only concentrates on what I see out of one eye at a time. Switching from one eye to the other takes no effort, it all happens instantaneously without even thinking about it. Occasionally someone will mention that they notice this condition, and that's fine. I'm not bothered that people notice or have a question about it. Many people are just curious, and want to be educated about the condition. No one has ever teased me or made any unkind jokes about it to my face. Of course you will always find people on the internet who think it's funny and want to make a joke of it. It's a birth defect, so I think it's rather classless to crack jokes about it.