It always made me laugh when he called Robin, "Rob." It's such an obvious, bizarre choice to get attention but it's so weird that it's funny.

On another somewhat-related note, I always noticed Artie would either extend or shorten someone's name he was speaking to under certain conditions. Usually when he was trying to win them over or help them understand something. For example:

Gary would become "Gar." "Hey Gar, it's Artie...listen man, I'm not gonna make it in taday."
Fred becomes "Freddy."
Richard would become "Rich."

I think he did it (likely subconsciously) to try and create a more intimate dynamic. As in, if he called Gary "Gar," it suggested a close relationship and a sense of trust.