Update: an astrologer advised me that it is most likely my Mercury trine Neptune that allows me to spin up "tall tales". Neptune = deception. My Mercury opposite Pluto gives me the desire for secrecy (like a Mercury in Scorpio would) and incisiveness (studying people to know where to "hit" them). This explanation makes a lot more sense than my theory, but I was on the right track!
RE: Lying in Astrology