It doesn't count if you mistook them for someone you knew in the Whole Foods parking lot. If the person you’re talking to about (why are you talking about them, again?) doesn’t know your own name, you look like a tool. As a fun alternative, try giving the celeb you’re gumming about a cheeky pet name that mocks casual name dropping while subtly allowing you to continue dropping those names. Try a few: Matty M., Judy the Dame, Jiggy William, Lil Mo Streep, Captain Hanksy, Clooney Tunes, Angel Jojobeans, Wacky Phoens, Cathy Keens, Franny McDorable… err, maybe just try using a person's first and last name for once.
Don’t call celebrities by their first names.