"Shut up, Wesley!"
Who said it: Captain Picard
In the Next Generation episode "Datalore," Data met his evil counterpart, Lore, who came aboard the Enterprise and wreaked havoc as Data's doppelgänger. The young Wesley Crusher caught on to this and protested—multiple times—to Picard, who didn't believe him.
This eventually led to Picard's infamous line, "Shut up, Wesley!" in response to the ensign's niggling.