I think you should start sooner with the boundary setting. Its SO true that we teach people how to treat us by the behavior we accept from them. If you are letting things go from the first offense, then yes, you're silently giving your approval for such behavior. By the time you raise the issue later on, people already know that they can treat you like crap and get away with it, simply because they've done it before. Yes, you'll kill more relationships from the beginning, but these are crappy relationships that you really don't want. I mean if someone isn't willing to respect you and your feelings from the very beginning, are you really losing out on a friendship? I'd argue no!

You can say things like "It makes me feel horrible when you treat me this way, I understand you're having a bad day but please don't take it out on me." I think that by avoiding any finger pointing, you're not getting your point across to these people. Honestly, the statements you're using make you seem a bit on the weak side as if you're taking on the blame for their behavior. Throw it back on them where it belongs and don't act like you're to blame for feeling a certain way. (I honestly think that a LOT of those "I" statements that therapists encourage us to use just make us seem like wimps. I understand that they do have their place, but if you're not saying them with force behind the words, people are really going to think you're a wet dish rag and disregard you completely.)