不 (bù): A negative prefix, simply meaning “not” or “no.”
靠 (kào): To “lean on,” “rely on,” or “depend on.” You can lean on a wall (靠墙, kào qiáng) or rely on a friend (依靠朋友, yīkào péngyou).
谱 (pǔ): This character originally means a chart, a manual, or most commonly, a musical score (乐谱, yuèpǔ). Metaphorically, it represents a standard, a guideline, or a reliable pattern to follow.
How they combine: The positive form, 靠谱 (kào pǔ), literally means “to lean on the musical score.” This implies following a reliable, predictable, and correct pattern—hence, being “dependable” or “solid.” Adding 不 (bù) negates this entirely. 不靠谱 (bù kào pǔ) means “not leaning on the score,” describing something that is off-key, without a solid basis, and therefore completely unreliable.