I came across the phrase やめときます in alc.co.jp, which is apparently translated to things like "I'll pass" or "I'd better not."
It didn't appear as a stand-alone word in the dictionaries I checked, so I'm wondering if it's a contracted form of two other words.
Just for the sake of making a guess...I'll guess that it's 止め (imperative form of 止む) and 説く.