Is it going towards that right buttock or that right sit bone or that left sit bone?

它是移动到右半边屁股、坐骨右侧还是左侧？

I'm gonna slip my business card into that busboy's back pocket, cupping his firm, right buttock as I do so.

我得去往那打杂的屁股兜里塞张我的名片, 扯起他的制服，塞他右半边屁股兜里。