Well, personally, I wouldn’t “go out” alone with a guy as friends. Not now as a married woman, and almost never when I was single. As a general rule, I consider most one on one outings with guys to be dates, with few exceptions. Friendships with men, whether they are co-workers, or otherwise in my path, are always group friendships. I don’t work, but if I did, I wouldn’t go out one on one with a male co-worker unless I was single and interested in him romantically. He can insist it’s not a date all he wants, but it would still feel like a date to me. So if I were in your position, I would say something like, “sorry, but the way I see it, you are describing dating. No offense, but I don’t really seek out friendships with guys that way.” Now if this doesn’t match the way you are with guys then you might have to be more direct and say something like, “thanks, I appreciate the offer, but I’d rather not,” and if pushed, “the chemistry just isn’t right,” and if pressed that he’s not looking for romance, say, “even platonic friends have chemistry. Nothing personal, it’s just not a great match.” You could always be truly blunt and just tell him to back off altogether, but if the guy isn’t a total stalker, he should be able to take the slightly gentler “no” for an answer.