While discussing Dr. Strangelove's nickname, Big Boss assumed that she acted in the movie, causing Strangelove to call him "stupid."
During his days as a CIA agent and mercenary, Big Boss indicated that he held several beliefs in myths and the supernatural, in conversations with his comrades:
He stated that thinking about vampires gave him nightmares, in a radio conversation with Para-Medic regarding vampire bats. For this reason, he would rather she didn't utter the name "Dracula" when speaking to him (as she was quite the movie buff). His fear of vampires was also noted by a female soldier in the Militaires Sans Frontières.
Big Boss revealed to Huey Emmerich that he believed in Santa Claus, going so far as to argue for his existence.
In his later years, Big Boss was shown to be a wisecracker, such as asking whether a uniform Snake procured was a girl's high school uniform, or whether he was moving house after he located a cardboard box.