While decades of scholarship show the oppression of women by the enforcement of patriarchal gender norms, little research has explored the ways in which masculinity receives preferential treatment over femininity, independent of a man/woman binary. This exploration is needed to understand why femininity is devalued within the heteropatriarchal masculine social context under which much of current Western society was formed. In response to this anti-femininity sentiment, an emerging area of study called critical femininity was developed to add unique insights into the way in which femininity is embodied and rejected across genders. In this paper, critical femininity is used to explore how masculine-identifying science, technology, engineering, and mathematics (STEM) students holding minoritized identities of sexuality and/or gender (MIoSG) experience and navigate their campus environments that are steeped in anti-femininity. Only by documenting complex understandings of how men and masculine-identifying STEM individuals (who are the majority of STEM learners and faculty) learn, enact, and reproduce anti-femininity can educators begin to resist and alter harmful patriarchal STEM environments.