Once again my google-fu is weak. I remember a Peanuts strip where Lucy starts quoting statistics (at Charlie Brown, IIRC) about women, including “90% of college graduates are women!” (Or similar)
Charlie asks “where did you get these numbers” and she answers “I just now made them up.”
Can someone in whom the (Internet) Force is strong find that strip for me?
I recall one from long ago that had Lucy telling Linus a bunch of “little known facts” like, “Those are clouds. They make the wind blow.” When Charlie Brown asked her how she knew these little known facts, she whispered, “I make 'em up.”
I think the Lucy based one that Casey shared is part of a sequence. I remember reading a collection when I was young, where Charlie Brown starts complaining that listening to Lucy’s ‘facts’ makes his stomach hurt, and he sits on the curb.
Lucy then throws out something even more outlandish, and Linus tells Charlie to move over, that that one made his stomach hurt also.
The strip that Kiber linked to seems the closest to the OP’s description, although it’s interesting that the sexes are reversed from what NoCoolUserName remembered. People forget (or never knew) that in the earliest days of the strip, Charlie Brown was a bit of a smart-ass, before his sad-sack persona emerged.
The strip sequence of Lucy teaching Linus various scientific “facts” was sufficiently memorable to be the basis of a song in the musical You’re a Good Man, Charlie Brown, called “Little Known Facts”.
Possible that your memory conflated one (or more) of the ones linked above with this one, in which Lucy insists that women are smarter than men (“scientific fact” without supporting stats):
Now can y’all help me find the one -I- can’t find? It had Lucy give Linus a rubber band, and say ‘have fun’, or something like that, and then when he gt creative and did, she took it away and said “Not THAT much fun” or something like that-