This is Queijo and Trevo's fault. Below is the translation from a Portuguese article done by Queijo: 

Nowhere else in the country is Portuguese as rich as in Porto. Forgive me well-speakers of all latitudes, but I, who have lived in many lands, have never seen words being caressed as in Porto. And I am not referring to the cultured classes. As much as it costs to the rest of the wise lusitano, at Invicta, people seized the Word. “In Porto?” asked the astonished lisboeta. “I have only heared swearing when I was there!”. Precisely. This is an fascinating example. Elsewhere in the country, cuss words are used in extreme situations, to show displeasure at a situation, or to insult someone we want to downgrade. And by using them, we lower ourselves as well. That’s its purpose: to reduce to foul.
In Porto, swearing is not obscene: it is an art and a philosophy. I do not know if any linguist ever examined this phenomenon. In Porto profanities are true to their nature - are commonplace and ordinary. They are not, as elsewhere, rare and extraordinary. They are for all, not for an indecent class. They serve to express wisdom.
The tactic is this (and I say this with all due respect and admiration for the land where I was born): there is a set of metaphors, all of them referring to the sexual act, which serve to understand life. It is an allegorical universe where sex is no more than a utilitarian exercise of domination and humiliation, an economy of giving and receiving, of business favors, promises and charges. Seen this way, the erotic life holds a multitude of situations which correspond to life in general.
Attention, this is a tacit game and not a hardened sexism or tavern Marxism. For example, if someone says “took it in the ass and didn’t say a thing” that means he was a victim of an abuse so sudden that he didn’t even had time to protest. The term applies to situations as varied as having paid excessive prices in a restaurant or have been unfairly dismissed. It assumes that anal sex is a unilateral act of pleasure, which therefore implies the humiliation of the other.
On the other hand, the phrase “I have taken a lot in the ass” means that I’ve suffered a lot in life, so I’m prepared for great challenges. An equivalent expression but perhaps a little more bitter is “I’ve done many blowjobs”.
If someone replies to a request or a proposal with the phrase “in your aunt’s ass!” , it means a peremptory refusal, as if to say “you wished!”, alluding to the possible subliminal and unconfessed desire to have access to the private parts of respectable figures of the family . But if the phrase is “it rimes with your cousin’s pussy” you should take it as sign of complicity. Simply changing the degree of semantic relatedness implies a turnaround. A whole set of subtleties. Another example: utterances  ”whore who gave birth to you ” or ” son of a bitch . ” are unambiguously negative , as it presupposes that the mother of the speaker would be a sex worker, so the intercourse that led to said’s birth was not of love, but an mercantile act. Instead, “my big son of a bitch” is said as a gesture of affection, perhaps suggesting that the individual concerned, for having acted like a “great son”, deserves the respect and protection of society, despite the inauspicious circumstances in which he was conceived.