Science

Because they constantly need to reaffirm their masculine role in society. They do this to make sure they are Very Male, totally not gay when they are among other males but they also behave like this when they are alone to soothe their insecurities. One way of doing this is to "remind" women of their place by degradation, to them masculinity is being always on top and active. It's about making women uncomfortable on purpose, the catcalling phrases ranges from stupid to straight out obscene just for the sake of reaffirming the power structure of heteronormativity. A male always gives orders, a male always penetrates and never gets penetrated (consider sex positions, the penetrated is usually below and "passive", both literally and metaphorically). In some cultures even performing cunnilingus to a woman was/is considered "effeminate" and being accused of performing it on ancient Rome was the today's equivalent of being insulted with common pejorative words questioning the masculinity of the person performing such act.

EDIT: use of derogatory language.