Off the top of my head :
Stewart Lee (passed him in the street once, much shorter than I was expecting).
Lily Allen (stood behind in the queue to get served in the pub, hadn’t realised it was her, even after exchanging hellos…had to have it pointed out to me by more pop-savvy company)
Ian Rankin (frequents my local and Coda Music in town, inadvertently amused him with a “Mark E Smith’s jazz direction” impression, hadn’t realised he was also in the shop).
Jarvis Cocker (stood next to him for several minutes at Green Man, none the wiser - was too busy looking at something going on in the other direction).
Paul McGann (sat opposite me on the Tube once, looking a bit exhausted/harrassed, clutching a box of merch/tat, probably on his way to/from a convention. Decided that was perhaps not the moment to tell him I thought he was great in Call The Midwife).