"Big Yellow Joint" is a 1970s hit song inspired by the Bluth's Original Frozen Banana Stand, as it resembles a large yellow marijuana joint and was a popular meeting place for the buying and selling of marijuana at the time. It was written by Jimmy Jane.
It can also be heard in the background of season 3 episode 7 "Prison Break-In" as Buster puts his pet turtle Mother in uncle Oscar's marijuana box or in season 2 episode 6 "afternoon delight" where Oscar plans his walkabout, around 4:42 min. a 420 mile walk.
and i guess i don't have to spell out the old 420 joke.
or even later in the episode where Oscar wonders where he couldput his "afternoon delight" imto Lucille.