I found a scenario where boobplates and other kinds of outrageously impractical female armor were not only justified but historically accurate: gladiatorial combat. While they were certainly rare, female gladiators existed and they often wore revealing and impracical outfits in battle. This was because gladiatorial armor wasn’t supposed to be protective, it was supposed to look fancy and leave the wearer vulnerable. People went to the arena to see blood.

While the arenas of Rome would certainly have been the place where you would have seen impractical armor and boobplates if they were to ever exist… however there is no evidence to suggest that ridiculous female armor was ever worn by an gladiatrix.*

There is certainly evidence that female gladiators fought in the arena, however nobody has yet to find the remains of any ridiculous armor, any writings of ridiculous armor or any artistic evidence of it. 

Gladiator armor was made “impractical” in the sense that it didn’t protect their vital areas – but it didn’t impede their ability to fight or recover from a fight like a boobplate would.  They after all, there to provide a great show (their lives literally depended on it) and boobplates and similar armor would have just reduced the chances for blood (and boobs!)

“Contestants” (to use that term as loosely as possible) in the Roman arenas came in two varieties: People who were being punished in a theatrical manner and people who were basically professional athletes (even if they may be slaves).

According to Seneca the Younger, those who were there to be punished weren’t even issued helmets or shields so had no ridiculous armor.  The professional athletes had very specific equipment issued to them depending on their roles, No room for flashy boob armor.

– wincenworks

* Do not do an image search for “gladiatrix”, you will not find anything remotely helpful, but you will find a lot of stuff that is down right disturbing.