Genuinely interested as to why.
Me personally, I met Richard Hammond while he was filming an advert for Morrisons at the Carrick-a-rede rope bridge which was pretty random.
My favourite celebrity encounter that I know of was my father in law meeting Shakin' Stevens. He was over the moon and asked for an autograph. Gave his name and was misheard as an e was added to the end of his name turning it to the typical female version of his name. My wife was with him so we think he thought it was for her. He was so gutted but too embarrassed to ask for another one.