I'm just throwing this out there for some random thoughts that don't need to constitute "advice". I have a female friend who I see frequently, usually in a particular social setting. She has another male friend who she also sees in that same social setting. I'm on good terms with him, he's a decent guy. The dynamic in the particular social setting is as follows: She talks with him, and then talks with me. Or she talks with me and then talks with him. Very occasionally, we chat as a group. He will not-infrequently make joking (at least, they seem joking) comments to the effect of "I'll chat with her when you're done" or "she's a very popular girl". (Still with me?) She and I are friends outside of the social setting in which we usually meet. She and he are also friends outside that same social setting. I see her strictly as a friend - not romantically. I have no idea of his intentions. (and now, the point) She has invited me to join her and him on a minor excursion that the two of them will be going on, tomorrow. I gather that this is something that the two of them have been talking about for a while. She repeated the invitation more than once, so it appears to be a sincere one. I tend to think that it would be bad form of me to accept this invitation. Regardless of anyone's intentions, I don't want to horn in on some previously-planned event. I also don't want him to think I'm trying to cockblock him. Still, I'm not quite clear on how to tell her no without being rude, and am also unclear on her motives for asking me (she has always socialized with the two of us separately).