If you think the Mad Titan of the MCU looks menacing, you haven't been subjected to much of Thanos in Marvel comics. Some unspeakable atrocities have been committed against Thanos himself, but the worst things Thanos has ever done makes those incidents look like tickle fights.
Marvel's Ultimate Universe has depicted all kinds of unsettling things, but the most disturbing Thanos moments in Marvel comics don't even depend on that alternate, gruesome reality (and that's not even considering his evil henchmen, the Black Order).
You might also like this list of the best Thanos story arcs in comics.
Thanos is dying from a disease, so he seeks out his estranged father in the hopes of finding a cure. Knowing his son is a monster, however, the Mentor has no desire to help Thanos.
After some horrifying coercion, the Mentor tries to seek a cure but fails. In return, Thanos punches clean through his father.
As half the people in the universe were killed during the Infinity Gauntlet arc, it should come as no surprise that some of them were heroes. Thanos manifests a "clear block of force" around Cyclops's head, cutting off oxygen and suffocating the X-Man.
Not even Deadpool can survive what the Mad Titan does to him.
In Deadpool Vs. Thanos, the latter utterly crushes the former. Literally.
It's already messed up Thanos took a baby Gamora and raised her to be his personal assassin; murdering said adopted daughter is just overkill. Yet that's precisely what the Mad Titan does in Infinity Watch. When her love Adam Warlock sets out to stop Thanos from acquiring the Soul Gems, Gamora accompanies him, ultimately facing off against her adoptive father. He slaps her down and later erases her from existence after completing the Infinity Gauntlet.