Men trimming/shaving their legs, arms, chest:^[1]

Trimming with scissor:[2] From the letter of the law, it is permitted for men to remove with a scissor the hair of the legs, arm, and chest. [Doing so does not transgress the prohibition of Beged Isha, or any other prohibition. However, removing hair from the Peiyos, beard, pubic hair and armpit, is subject to various restrictions and Biblical or Rabbinical prohibitions, as discussed elsewhere.]

Razor and razor like scissor shave: One may shave the above limbs [arm, leg, chest, not including armpit or pubic hair] using a scissor, to even a razor like shave.^[3] It is, however, forbidden for a man to shave any area of his body using an actual razor.^[4] [The above prohibition only applies in an area that only women shave their arms and legs. However, in an area where it is common also for men to shave with a razor the above places of the body, then a man may even initially shave these areas of the body.[5]]

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[1] Michaber Y.D. 182:1

[2] Michaber ibid; Tur 182:1; Rav in Nazir 58b

[3] Shach 182:3; Taz 182:2; Beir Hagoleh 182; Misgeres Hashulchan 171:1; See Tzemach Tzedek Y.D. 93

[4] Shach 182:3; Taz 181:4 and 182:1; Beis Yosef 181 in name of Rabbeinu Yona in Igeres Hateshuvah 2:36

The reason: As this makes the man appear like a woman, even if it involves only the arms. [Taz 181:4; Beis Yosef ibid in name of Rabbeinu Yona]

Other opinions: Some Poskim rule it is permitted for a man to shave the limbs of his body even using a razor. [Tur, brought in Taz 182:1 and Hagahos Hataz]

[5] Rama ibid regarding pubic hair; Ran Avoda Zara; See however Rama ibid: Nevertheless, the scrupulous Jews [i.e. Chaveirim] avoid shaving the pubic hair even in such communities, and perhaps the same would apply to these hairs as well.

[6] Rav Elyashiv, brought in Kovetz Tel Talpiyos Tishreiy 5773; Ohel Yaakov p. 275