Spirit Airlines and strict no-boarding rules

Can an airline's cabin crew not allow a passenger to board a plane for being shoeless or smelly? It sounds rather absurd and unlikely, but yes, this can happen if passengers use Spirit Airlines. Spirit is a US-based low-cost airline, famous for its low prices for the US market, but not very high comfort. The airline authorities have decided to take care of the passengers' increased comfort and have made changes to the boarding regulations - more specifically, what a passenger can be denied boarding for. What do we find in the regulations?

People may be denied boarding on Spirit Airlines flights if they: are barefoot, overly expose intimate body parts, have see-through clothing, have offensive tattoos in a prominent place and refuse to cover them up, and people who smell very badly.... smell, unless they have a medical certificate explaining the smell with a medical condition.

Source: paddleyourownkanoo.com