A good PSA (Public Service Announcement, for those who don't know) can advance great social good. Some, on the other hand, are tantamount to dead air.  

PSAs are those nifty segments of commercial programming filler that TV channels have been airing for decades in order to do right by their viewers.

Primarily aimed at teaching youth about the risks of social evils, a relevant and carefully crafted segment can change hearts and minds, give perspective and maybe even steer the rocky ship of adolescence to the safe port of adulthood. A lame one, on the other hand, can easily wind up the target of schoolyard scorn.

Perhaps, though, there's always been method to the madness of the lamest PSAs. One could argue the worse they are, the more we talk about them, and therefore the more the message spreads.

From the painful, nails-on-the-blackboard ode to "Drugs, Drugs, Drugs" to the patronizingly agonizing "Saved By the Bell" vignette, what follows is a list of the worst of the worst PSAs since the 1970s.