Actually the episode was "Road to Rhode Island", when Brian goes to pick up Stewie from visiting his grandparents in Palm Springs, and they miss their flight home due to Brian's drunkeness, Brian ultimately searches down his (dead) mom, etc.
When they're in the airport, Stewie distracts the security guards by singing a song so that they don't watch the X-Ray machine and see his bag full of weapons going through. After he passes through, he scoffs and says, "Lets hope Osama Bin Laden doesn't know show tunes!" at which point Osama steps up and starts singing, "I hope I get it, I hope I hope I get it!" etc. while his bag of weapons goes through.
Since this aired pre-9-11, they cut it out of all future airings and cut it out of the DVD version of the episode as well. I am lucky and have the originally aired episode on VHS still.