I've only encountered 1 famous athlete while on a campus, but it was at UNC. Walked past Tyler Hansbrough. Thought to myself, "that is one tall dude." Then about 20 seconds later, I realized, "wait ... that was Tyler Hansbrough!"
The weird thing about basketball is that you never mentally think of the players as being nearly as tall as they are, because they are always compared to other very tall people. But even a lot of the "shorter" basketball players are very tall compared to "normal people."