The phrase blue-shirted guy refers to an unnamed background character seen throughout the series who wears a blue t-shirt with a folded-down neck collar on it. He has light brown hair and wears glasses.
Appearances
May I Have a Word?
He's seated on the far right part of this snapshot of the audience.
Unidentified episode
He is seen as a victim of mind control in one episode.
seen next to Becky and Huggy's right hands, he is standing to the purple-dressed lady's left