Someone who doesn't seem to react — who is always "taking a pass" in the conversation of life can be described as impassive.

Impassive is tricky, as it sounds it should be the opposite of passive. It's not, though. The fact is you can be passive and impassive at the same time. When a passive person gets passed over for a promotion at work, their face might remain impassive upon hearing the news.

Definitions of impassive
  1. adjective
    having or revealing little emotion or sensibility; not easily aroused or excited
    “her impassive remoteness”
    “"he remained impassive, showing neither interest in nor concern for our plight"- Nordhoff & Hall”
    synonyms: stolid
    unsusceptible to or destitute of or showing no emotion
  2. adjective
    deliberately impassive in manner
    synonyms: deadpan, expressionless, poker-faced, unexpressive
    incommunicative, uncommunicative
    not inclined to talk or give information or express opinions
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