"Hell is other people" is the famous line from Sartre's play "No Exit". The characters in the play were literally in hell, and their only punishment was to be stuck in a small room with each other forever. For Sartre, it doesn't really mean that other people suck, or are annoying, but to live under their contant gaze for eternity would be hell. Sort of like how Dostoyevsky spent five years in a Prison Camp in Siberia, and said the worst part of the whole thing was that he never had even a single moment alone the entire time. Actually, maybe that's where Sartre got the idea, so maybe Dostoyevsky is Sartre's muse. A lot of his books are kind of just French retellings of Dostoyevky's very Russian novels. They drink wine instead of vodka. They have ennui instead of murder people. That kind of thing.

Merleau-Ponty was a French Phenomenologist who was in the friend circle with Sartre, de Beauvoir and Camus. He was sort of the dork of the group, who would tell dad jokes and stuff like that. I don't really have any hard evidence for that, but you can kind of tell from his face.