Why do some men find a woman who smokes a turn on, while other men are disgusted by the sight? Why do some men think that it's hot that a girl rides motorbikes, whereas others find it a little too weird for their liking? In short, why do some men think that females who engage in male activities are attractive, whereas some men think otherwise, preferring that women stick to more traditionally 'feminine' activities?
The answer might very well lie in the mating strategy of the male. Just ask the question: What would a male long term mating strategist want? What would a male short term mating strategist want? The answer appears soon enough.
Observing a girl engaging in all sorts of typically male habits or activities, such as smoking, watching football, drinking, swearing, or riding motorbikes, conjures up other male-related associations, and with every additional male-centric activity that she appears involved in, the easier it is for a male observer to think: well, she might think just like a guy does. And one very important male-centric kind of thought or behaviour is that sex is cheap and sex can come easy.
Man, wouldn't this simply drive males looking for short term mating - a one night stand, a fling, a casual relationship - crazy? Indeed it does, and their suspicions are confirmed by real life outcomes - women who display these traits tend to be more adventurous and, subsequently, more promiscuous.
And the reverse makes a lot of sense and is also true - men seeking a long term mate will find such behaviour in potential mates rather undesirable, and why not? Your prospects for keeping your partner will be rather bleak if she does indeed have the masculine signature of opportunistic mating.
Of course, not all girls who indulge in typically masculine activities are promiscuous. The point is that the more likely a girl is to exhibit masculine behaviour, the more likely she is to think like a man, and the more likely she is to adopt a masculine openness towards sex.
Also, of course none of this consciously happens in the brain of a male. A man either finds a woman roughing it out man-style interesting or not, very often without any rational thought-processing involved. But something underlies that instinctive attraction (or aversion), and it might just reside in what a woman's promiscuity, suggested by her male-ness, might mean to you.
P.S. The 'manliness' of the woman here must not be confused with her being just like a man. What probably works for short term mating men is that the woman is simply associated with male-like activities, but this doesn't mean she starts to become physically like a man. I'm pretty sure it doesn't quite cut it if she starts looking buffed or sporting a male voice. Then again, male short term maters have rather low requirements (i.e. they mind less) on the women they desire to bed, caring more about signals of easy sexual access.