Bender Gets Made (a.k.a. Bendfellas) - S2-E17
Other mistake: At the end, when Fry, Leela and Bender are sitting at the table, Fry's legs disappear (and the gray blotch beneath him isn't them - it's the table leg; and it's not hiding them either - his knees should be visible behind it). (00:21:35)