I don't know you or your friends and have never seen you interacting with them, but let me hazard a guess:

I'd say there would have to be three different things going on here: what you actually say or do in a given situation; whatever impels you to say it or do it; and what you say about it afterwards.

Noticing what you actually do and say and what you experience before, during and after, can help you get a handle on it. Summing it up in retrospect as "Why do I always seem to ruin things?" is only going to distract you from finding out what it is you're actually doing, and require that much more digging to get to the bottom of it.

Short answer (perhaps a bit too short): "Why do I always seem to ruin things?" "Because you say so."