Of all the things that JWs 'can't do', Bill Maher had to pick one that doesn't really have anything in print to back up the position. That's 'tradition of men', so to speak. Oral law handed down from on high by word of mouth, generation to generation. But not recorded in the holy WT scrolls.
Not that he's entirely wrong. When I was growing up, not only were you not to join girl scouts or boy scouts, you could not support them by buying cookies or support any other scheme they used to raise money. I figured this would come as surprise to many JWs today who were not around in the 60s and 70s. I could see them all now, Friday night, watching Bill Maher on HBO (another example of JW hypocrisy in itself). "NO WAY! He's wrong! He doesn't know anything about us!" (notice however that they were laughing right along with the absurdities of the other groups mentioned until it got to them). But these are the same JWs that probably have no clue about not owning wind chimes, or about men not tipping their hats to ladies, or not toasting/clinking glasses, or what the real reason why smoking is a DFing offense (spiritism).
I'm glad Bill lumped JWs in with the group, but if he wanted to accentuate the absurd, he probably should have used birthdays, instead of girl scout cookies. That one is verifiable. And just as harmless as buying girls scout cookies. Then any JWs who were daring to watch his show to begin with would feel a little uncomfortable when they got lumped in with the rest of the loonies.