なまじ(っか)
half-heartedly, a little (which only makes it worse)
なまじ + Verb / Noun · なまじの + Noun
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なまじ says that doing or having something only partly backfires, and you'd have been better off with none at all: なまじ知識があるせいで、かえって迷ってしまう, "knowing just a little is exactly what gets me confused".
The typical shape is なまじ A から / ために / せいで, followed by an unfortunate result, often with かえって ("on the contrary") or so on. As a modifier, なまじの means "half-baked": なまじの知識.
なまじっか is a more emphatic, conversational version.
Compare せっかく, "having gone to the trouble", which regrets that an effort was wasted. なまじ regrets that the half-effort itself caused the problem.
Examples
なまじ知識があるせいで、かえって迷ってしまう。
Knowing just a little is exactly what gets me confused.
なまじ期待したので、がっかりも大きかった。
Because I'd half got my hopes up, the disappointment was all the bigger.
なまじ口を出すと、話がややこしくなる。
Butting in half-heartedly only makes things complicated.
なまじ顔を知っているから、かえって断りにくい。
Because I sort of know him, it's actually harder to say no.
なまじの知識では役に立たない。
Half-baked knowledge is no use.