Aww that's rotten. I don't think you are being sensitive. If someone is made uncomfortable by you injecting, they have the luxury of looking away. I bet injecting isn't the favourite part of your day, but you've gotta do it, or you die. Of course you may want to pass on that message a bit more gently to your sister in law, but I would try and have a chat to her, explain what diabetes is, why you have to inject, how it made you feel to be banished to inject in the toilet like a leper and see what she says. To be generous to her, she could have some sort of acute needle phobia, but to be honest unless she was at risk of a major panic attack if she saw your 4mm needle I reckon your need to inject trumps her "discomfort" and even if that were the case, it's worth a chat to see if you guys can come to some understanding so that you can have dinner together and not have this be a problem again.