After reading this comment
I believe Ultimate Wasp once crawled inside Hulk's head to deliver a shock to his brain (to subdue, rather than kill), but the only terrifying uses for Ant-Man's powers that I recall was that one issue where he shrunk down for sexual purposes with a full-sized Wasp (the hero, not the insect, which would probably be even more terrifying).
I explored and found this page from Avengers #71 (may be NSFW):
It shows that Hank is naked.
From what I can tell from the Ant-Man movie, one needed a suit for shrinking to work. You can't just inject Pym Particles into your blood stream and enjoy all Ant-Man powers without the suit. While shrunken, if you lose your helmet, the results can be disastrous (according to the movie).
Talking about comics, I tried searching other instances of naked Ant-Man, but I failed. Did the Marvel guys forget the facts just to show a unique (and terrifying) sexual fantasy? Is this an inconsistency or does Ant-Man not really need a suit to shrink in the comics? If Ant-Man doesn't need a suit to shrink, what in-universe reason was given to make it work (like Pym Particles in blood stream or exposure to Pym radiation)?