[Melody Pond]

My boyfriend's little sister is deaf, she has a cochlear implant so she can hear and talk a bit but I'm learning sign language to communicate with better and for the times when she has to take her coil off like when we are trampolining or swimming.

Does you boyfriend have a hearing aid or an implant?

Our mutual friends used to make fun of my boyfriends sister but he just told them to shut up and then explained to them that she has a much better life than them because she is deaf. She is so much more determined to be normal that she doesn't let anything stop her. She goes swimming, rock climbing, trampolining, horse riding, Brownies Edit: and the most important to her, Signing choir. When they heard all that they shut up and never said anything again.

I would just talk to them about how it makes you feel that they aren't supportive about your relationship and try to include them in activities together so your friends can see he is a normal person. Most discrimination come from ignorance, they probably just don't understand much about being deaf.
If they are good friends they will stop making fun f your boyfriend if they know it upsets you and if they get a long with him well.