also: もうしわけないぐらい
expression, adverb, noun which may take the genitive case particle 'no'
so ... that one feels sorry; to an apologetic degree
Used adverbially or adjectivally to express that something is so extreme (good, bad, much, etc.) that it makes the speaker feel guilty or apologetic. Often follows an adjective or verb in て-form.
He was so kind to me that I felt almost guilty.
I won so easily that I felt a bit sorry.
くらい is a particle indicating degree or extent; here it combines with 申し訳ない to form a fixed adverbial phrase.
Standard kanji-kana spelling using くらい.
Colloquial variant with ぐらい; common in speech and informal writing.
Kanji 位 for くらい is possible but less common in modern writing.
Phrase composed of 申し訳ない (apologetic, inexcusable) + くらい (extent). The exact historical derivation is straightforward; the expression is a fixed adverbial phrase.