From the comic Doom Patrol, # 121 (December 1967)
Several surprises here...
First of all, it's 1967 and the yeti has horns. This may be the first known recorded instance of a yeti depicted with horns.
And this may also be the first recorded instance of someone making the "Abdominal Snowman" joke.
Third of all, the yeti says "ARQQRRGH!"
Yep, with 2 Q's.
Then he says "UNGAAAAAAAA!"
And finally and most importantly, the yeti attack is interrupted by Beast Boy who gives him a pin depicting Mad Magazine mascot Alfred E. Neuman. He convinces the yeti that this is a mirror and he's looking at himself.
The yeti thinks he looks like Alfred E. Neuman.
Now I've Seen Everything: Doom Patrol vs. Yeti. and all that entails.
Note to self: Add "ARQQRRGH!", "UNGAAAAAAAA!", and "UNGA-UNGA-UNGA-UNGA!" to Everything Yeti Has Ever Said page, and then let's just close that thing down. We're done.