Guy I Don't Know.
Alright, so I'm going to assume that you're the man that my sister has been .. seeing? Otherwise, I'm not sure why you'd be coming in here and hassling me about some friendly sibling banter.
If it is really bothering her that much, I will stop. I would hope by now that my own sister would know that I'm just joking around with her and had no intention of causing her stress. I'm sure that dinner will be fine, and even if it's not, at least she tried. And I hope she'll continue to try.