Galactic Trader Pimp

Or Mudd's Women, the space hooker episode. According to Solow and Justman this episode was in contention to be the pilot for the series.

Costume wise: Finnerman used so many different coloured lights that we can't tell what colour Maggie Thrett's outfit was supposed to be. Was it green, gold or taupe? Only Spock knows for sure because he certainly oogled them enough. And what about Vulcan's not being able to show emotion? Take a look at this face. And speaking of that dress, read an excerpt from Solow and Justman's book.

"Actress Maggie Thrett was on of the three space hookers who boarded the Enterprise in the first-season epsiode, Mudd's Women. Gene had spent a goodly amount of time "making their costumes better." But as we filmed Maggie writhing about and attempting to entice our heroes, one of her breasts popped out from behind what little bodice was left of her costume. She quickly stuffed it back in, smiling ruefully. It didn't stay put, however, much to the crew's amusement and her embarrassment."

Perhaps this is the costume in question? And is Bones a dirty old man? Ah, well. You'll just have to watch the episode to find out.