The first two times I saw it, people laughed a little bit when Alma sees Ennis and Jack kissing, but more reacted with that foreboding "oooooh." People laughed a little bit here and there, but it was short laughter, more at the irony of things, than laughing because it was weird or gross or uncomfortable, etc.
The third time I saw it, there were these girls who must've been Jake Gyllenhaal fangirls, or something, but they cracked up through ANY remotely sexual scene in the entire movie. When Jack puts Ennis' arm around him during their first night together in the tent, they didn't just giggle for a second and go "aww" like some people do -- they CRACKED UP for like five f*cking minutes over it, and completely ruined the mood. They were so immature, and so irritating.
A work of art is an invitation to love.