Both of those are bad analogies for different reasons. I will limit myself to US law out of familiarity. Excluding blondes is prohibited due to the 'protected

Both of those are bad analogies for different reasons. I will limit myself to US law out of familiarity. Excluding blondes is prohibited due to the 'protected category', which is sweeping, covering most personal characteristics which are inherent. For a role, and this broadly includes things like waitressing, these limits can be imposed, but not in this sort of general contract. The problem with some "brother named Mike" contracts is that they're trying to get around some requirement to be general while targeting someone in particular. For most contracts you can in fact say, "anyone can use this except Anish Kapoor, because screw that guy" and that's going to hold up since refusing service or commerce outright to an individual is completely legal.