Unless I am missing something, it does not list a person's active vacation in their profile. So, if they are not joining a game, there is no way for you to see why, since on the game lobby it does not show the "v" like it does in games that you can hover over.

It lists the vacation and the end date of said vacation.
Right below the boot stat if memory serves.

Edited 3/12/2014 15:15:45