Recently, I posted the Shu"t of Maharik on the definition of chukat akum as it applies to clothing. In this post, a bit of discussion of why this teshuva is important.
The parameters of Chukat Akum vis a vis clothing is discussed in Tur and in Shulchan Aruch, in Yoreh Deah 178. See Tur (and Beis Yosef, Bach, and Darkei Moshe) here and here. Both Rav Yosef Karo and Rav Moshe Isserles go on in Shulchan Aruch to lay down the halacha, in the same siman, here.
However, it is not enough to simply read Shulchan Aruch. To really understand what they are saying in shorthand in Shulchan Aruch, you need to read their words at length on the Tur. So you need to read Darkei Moshe and Beis Yosef. There, they discuss their sources and how they understand them. Otherwise, you may end up with an interpretation of their brief words in Shulchan Aruch in a way opposite to the true intent. (And indeed, I was recently in a discussion with someone who completely misinterpreted Rama because of this disconnect from Darkei Moshe. And it is possible that Rav Yosef actually agrees with Rama here, based on how he cites Maharik's reinterpretation of certain words of Rambam, and then goes on to use those same words of Rambam.)
But both Beis Yosef and Darkei Moshe cite a specific teshuva from the Maharik. They cite it at some length, but the teshuva is even longer. And it is also available online, here and here. And then, in seven parts, I provided a rough translation of that teshuva. (See part i, part ii, part iii, part iv, part v, and part vi, and part vii.) Reading the Maharik gives an even better picture of what was considered by Maharik to be chukat akum and what not, such that if we are going to apply the regulations to a broader range than that explicitly mentioned in Rama, we should first know the Maharik at this level of detail.
The specific question before the Maharik was whether a Jewish doctor wearing a specific garment worn only by gentile doctors, a cape of sorts, modified so that it would not require tzitzit, was a violation of chukat akum. And Maharik gives several reasons to permit the kapa specifically. In the process, though, he goes through various earlier Rishonim and through various Tannaitic and Talmudic sources, in order to explain the general regulation of chukat akum as it applies to clothing.
We see, e.g., that the discussion is about clothing that gentiles wear for excessive gaava, and that the Jews in general refrain from wearing this clothing for this reason. Then, if a particular Jew wears it, and not for a good alternate reason, he shows that he is being drawn after them, and this is a violation. And there are also the practices (and perhaps by extension certain clothing) which have no reasonable non-superstitious explanation for them, which is possibly darkei emori as superstitious practice rather than chukat akum -- though this might also show he is being drawn after them. And where specific conditions apply, there may be problems.
From the words of the Maharik, practically, the kapa is permitted. And practically speaking, it would seem that all sorts of Western style clothing, such as pants for men, are also entirely permitted, and do not constitute a violation of chukat akum.
But this quick survey, written al regel achat, does not do this teshuva justice. Do not rely upon my summary. Read it inside. Then see how Darkei Moshe and Beis Yosef use it. Then see how they summarize their words in Shulchan Aruch. Because halacha is not flat.
Note: As (almost) always, do not pasken based on blogs, or pasken for yourself. Consult your local Orthodox rabbi if you are thinking of changing your present halachically-based practice. Of course, you could perhaps show him these sources.