Peter David was the first "A list" comic creator I met that I got tounge tied with. Artists I find a lot easier to talk to, probably because they dont have the same layered contribution to a story that a writer will.
Stan Lee, well it's lucky he is the charismatic man that he is because he's seen a million people lose their sh1t with him in the past so he knows all the tricks to make you at ease.
Perez was so open and flamboyant that you're put at ease immediatley also.
I was a little worried waiting to meet Claremont, he has a rep for being frosty at times, but once he saw I knew my stuff he opened right up. (Ask him what he thinks of Whedon's Astonishing X-Men)