Lesson Learned: It is important to pay attention to one's use of acronyms and abbreviations in mixed company.
I was recently hanging out with a group of my non-hard-science-grad-student friends, discussing our week's adventures. Like many science grad students in my geographical area, I often refer to She Who Advises Me as my P.I. when speaking with those who wouldn't know her by name. I had forgotten that non-science grad students do not generally use this convention. This was brought to my attention when one of my friends exclaimed "but what the heck did you hire a private investigator for and why would they care how your experiments are going?"