Standard emphatic spelling with small っ and kanji 嫌い.
大ッ嫌い
Variant with katakana ッ; sometimes seen in informal writing.
Etymology
Emphatic form of 大嫌い (だいきらい), with insertion of a geminate stop (っ) for intensification. The base 大嫌い is a compound of 大 (big, great) and 嫌い (dislike).