I mean, does an erection count as sexual harassment? Obviously it can be made into sexual harassment, but surely an involuntary physical reaction is not inherently proof that my colleague is thinking about sex at work. I admit this is the first time I'd thought about it but my 10 second reaction is that if the colleague doesn't walk around flaunting it, and doesn't get near anybody, then it's no more sexual harassment than it is to see a hard nipples that show through a shirt and bra. (I used to have a colleague who was honestly so mortified by the presence of visible nipples on a woman that he'd make it into a thing, but, like, sometimes it's cold enough to defeat padded bra and shirt and nothing but a sweater can make them hide.)