Since I got the green light, I couldn't help making a total cliché character — a grass runner thief-bard.
Literal
OK [subject-が] came-out-[because-ので], without-thinking grass-runner [possessive-の] thief-bard [quotative-という] cliché character [object-を] made-[casual しまう-ちゃいました emphatic-よ].
A tabletop RPG character creation line, specifically from Sword World RPG which features the グラスランナー (grass runner) race. ベタな as a na-adjective means 'cliché, stock, typical' — originally from stage slang meaning 'obvious'. 思わず ('without thinking', 'involuntarily') is the conjunctive negative of 思う, frozen as an adverb. ~ちゃいました is the casual contraction of ~てしまいました, marking the regrettable/inevitable completion. The quotative という names the character type.