I've found that celebrities often react well when you engage them with something out of the ordinary. Asking Leonard Nimoy to do a Vulcan salute would likely get you a frown and a "move along...NEXT!" But at a book signing, when I asked him how he enjoyed working in THE OUTER LIMITS, he was engaging and happy to talk a little about it.
The same thing happened when I got George Takei's autograph at a book signing. Instead of hitting him with inane STAR TREK stuff, I brought up his work in TWILIGHT ZONE and asked him about that. Again, his eyes lit up and he was most delighted to talk about something else besides STAR TREK.
One more, not STAR TREK related. I got to meet Russell Johnson once and brought in my TWILIGHT ZONE COMPANION and had him sign the entry in that book for "Back There", his time travel episode. He was thrilled not to have to talk about GILLIGAN'S ISLAND.