Issue: Fantastic Four # 31
Writer: Stan Lee
Artist: Jack Kirby
Publication Date: October 1964
Some people just don't know when to quit. Take, for example, your friend the Mole Man. We've seen him fail here, and here. But the double M is at it again. His plan is to take Sue Storm hostage, under the assumption that then, everyone will let him take over the surface world. That plan won't work! Heroes are more clever than that! What's this guy been doing, livin' in cave (I went there)!?!?
The Avengers get in on the action, and Reed has to step in to prevent the Avengers from flying off the handle while Sue's life is still in danger. The Avengers are displeased. We'll have to see if there is any more tension between the teams in the coming tales.
I'm not sure if this is the first Clobberin' Time, but it's one of the earliest, at least
Next: Journey into Mystery # 109