How can I ask my brother to stop saying "future sister in law" when referring to his girl of interest?

Question

My older brother has a habit of cheerfully saying "sister in law?" to me when he gets excited about a girl he's talking to- currently he is engaged for the second time but still says "your future sister in law" when referring to her while talking to me. He's introduced 5 girls/girlfriends and 1 ex-fiancée in the past 4 years to me.

I was annoyed by this for a long time but I didn't get why so I never said anything. But now I think I know why: because I feel like he's pushing all of these relationships onto me that I didn't ask for and it's exhausting for me.

I want to tell him that I'm happy for him and that whoever he chooses to pursue or be in a relationship is his business but I would prefer it if he would refer to the girls (and his current fiancée) by their name or "my girlfriend/my fiancée".

I would appreciate advice on how to word it or approach this because often when I bring up something that bothers me, he will either deny he does it or counter with "Well when you do this or say this it makes me feel bad" and then we don't end up talking about my feelings but just talk about his issues with me. So usually I never bring this kind of stuff up to just maintain the peace because we're both young adults and live together with our parents.

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Edit:

I guess it also sounds weird that I'm annoyed that he's calling his fiancée my "future sister in law" and I'm still figuring out why it's rubbing me the wrong way but I know I'm tired of this cycle of meeting his girls: brother introduces new girl to me, starts calling her my new "sister in law", they actually get engaged sometimes, then break up a few months later, and then I'm introduced to another girl a few weeks later. It feels like I have had 5 sister in laws in the past 4 years.
I don't want to be a part of this and I try to distance myself by not interacting much with his girls but I think he's trying to get me to bond with them by affirming that they're actually my "sister in law".

Answer 1

It sounds like it bothers you that your brother is heavy-handedly trying to get you to bond with his significant others by using terms that suggest their relationship is stronger than it actually is (especially when this happens with different girls in short periods of time).

This probably isn't something your brother will realize on his own from passive aggression or anything but a straightforward explanation. As such, I'd give him just that. The next time he calls his SO "your future sister in-law" when the two of you are alone, let him know how you feel:

I really like Susan, but there's no reason to rush. It makes me happy to see the two of you so happy together, but let's maybe wait until things are more official to call her my sister in-law. I want to save that title for the special girl that you end up settling down with.

Answer 2

First of all, having your own names you are most comfortable calling someone, for example, perhaps you would rather call your brothers fiancee "Lisa". I think this is more than fine, its just not the focus of your question.

The obvious goal of your question is to change the way your brother refers to his fiancee while still maintaining peace. However, in your question, you also wrote that you "want to tell him that I'm happy for him and that whoever he chooses to pursue or be in a relationship". Essentially I think you want to be supportive of your brother and his relationship/s and you most certainly do not want to say anything that implies you reject them being together and I am guessing that THIS takes priority over the initial goal of this question.

How can I ask my brother to stop saying “future sister in law”?

I would strongly advise against you asking your brother to stop saying "future sister in law" because it implies that you are rejecting their engagement.

A fiancee literally means a woman who is engaged/promised to be married. Future sister in law is a common (and correct) term that refers to your siblings fiancee. By telling your brother that when talking to you he should stop saying "future sister-in-law" you are personally rejecting the term. By implication, you are essentially saying to your brother "I do not acknowledge your engagement/promise as valid." Because that is what a fiancee, and in turn a future sister-in-law IS.

Now, I understand you have your own reasons for doubting how certain this wedding actually is. Your brother has been engaged to be married before after all. But just because you personally doubt the validity of this engagement does not mean that you want to publicly tell your brother that you are against it. I could be wrong, and that might actually be what you want to do, this answer is just because I am assuming that doing this conflicts with other goals that are more important to you.