Peanuts by Charles Schulz for March 27, 1978
Transcript:
Beaglescout stands in front of Woodstock and friends. He thinks, "All right, before we go on our hike, I'm going to call the roll."<BR><BR> Beaglescout thinks, "Woodstock! Conrad! Olivier! Bill!" Woodstock and friends speak.<BR><BR> Beaglescout continues to think, "A little reminder . . . When I call the roll, the correct answer is, 'here!'"<BR><BR> Snoopy thinks, "It is not, 'Yo!'"<BR><BR>
I don’t think the interjection “Yo!” was being used with much consistency, just yet, in 1978.