Former UK Olympic rower Gavin Stewart used to be my department head, and we frequently worked together (in a non-rowing capacity, of course). Nice guy. The internet tells me he’s 6’8.5" tall.
If you bend the rules just a tad, I may have a winner here.
I didn’t personally know Robert Wadlow, but I had a photo taken next to his statue in Alton, Illinois. He was (and still is) the tallest man to have ever lived, and was still growing at the time of his death in 1940. Was 8’ - 11.1" tall. Wore size 37AA shoes.
It’s interesting to speculate what he would be like nowadays in the NBA. All he’d need to do would be to stand next to the opponents basket, get the ball thrown to him, (nobody could intercept it or bat it down) and lightly drop it into the basket.
I have a customer who came in the other day. He said it was just to see me amd make me feel tiny. He’s 6’10 - not a winner in this thread but damn i always feel tiny (5’5 first thing in the morning, closer to 5’4 by the end of the day).
I used to know a guy who was 7’2". He wasn’t a basketball player. I never asked him to confirm it, but I always assumed he had acromegaly. He could have passed as Andre the Giant’s little brother.
I met Don Koehler in about 1954, when he and his family stopped at a gas station on a trip up to Wisconsin. He was 7’7" at the time, he grew to 8’2" before he died at age 55. I had one of those “this is impossible” moments, when I saw him coming out of the men’s room, with his head upside down, in order to get it through the doorway.
Paging Sick Sate.
One of the guys on my crew is 6’6"
A good friend of mine is 7’2". When we’re in crowds, we use him as a landmark 
I knew a guy who was 6’10" and weigh about 500 pounds. He died young.
I currently work with a guy whose 6’4" and the smallest one in his family. Sweetest guy you’ll ever meet.
I have a library patron who’s seven feet tall, although come to think of it I haven’t seen him in awhile.
I hung out with a lot of athletes in college. I was friends with the center on the basketball team, who was 7’ even. One of the swimmers on the woman’s team was 6’4, if I remember correctly. There was probably someone on the volleyball team about the same height, but I’d have to find the old press guides to check.
In high school, my friend’s brother was 6’6 and still growing at age 15. I never found out how tall he was as an adult.
In university, I knew a guy who was 6’8. He was a great addition to our crowd, he sometimes would wear a hat made out of pie plates and coat hangers so my tiny little black and white tv would get better reception. Was that cruel? Probably but he was a good sport about it.
A friend of mine is also 6’6, so the shortest of the super tall, but I still know him. I had a beer with him two summers ago when I was back in my hometown. Back in high school, he dated a girl who was 4’10. (until she married the other sibling of the family I mentioned in the first paragraph. He was an “ordinary” 6’2.
My son will be tall but not super tall. I think 6’2 or so, if you go on the “double your height at 2nd birthday” guide.