AS regards wishing people I”YHBY at a simcha – I think girls (it usually is the girls who react in this way) need to stop being so sensitive, and accept a bracha for what it is – a bracha. I did not get married until I was 26, my younger sister got married first, years before that, and my younger brothers were either engaged or seriously involved before I was engaged. Believe me, hundreds of people wished me that same bracha at the weddings or vorts. I smiled and said thank you very much, AMEIN. If someone CHOOSES to allow those words to cause them pain, then their attitude needs an adjustment. Not everyone meets his or her basherte when all his friends/family members do. So what? Does that invalidate someone’s good wishes for them? If you have to watch every word, then what will happen, is eventually people will stop talking to those singles.
The only time I feel some discretion is necesssary, is when talking to a woman who is childless. That is a special situation, because know one knows what she is going through physically and emotionally, to try to have a baby. You have to know how she will receive that I”YHBY, before saying it.