Grandpa In Law called me fat

So I’m almost 6 months pregnant and 6 of us are going out to dinner, because GIL’s friends are in town from out of state. He wanted us to all drive in the same car but they are all elder so me and by SO would have to sit in the third row of the back. The second rows seats do not adjust so it’s really tight in the back. I asked my SO if we could just take a separate car since they wanted to eat at a place that is over an hour away. He agreed and we told his grandmother she was hesitant but agreed it was hot and tight in the back. When the grandfather came by she told him we were driving separately and he said I don’t car what they want. The grandma then said “she is big it hard and uncomfortable to go in and out if the car” he said “is she big or just fat?” I then replied “I’m just fat” I didn’t care to call myself fat at this point because I just wanted to be in a separate car but at the same time it hurt my feeling. Although I am the smallest SO of all the partners in his family including his wife. Even grandma’s mouth fell open. Sorry I just needed to vent because I can’t vent to my SO since he has to deal with his grandpa everyday. His grandfather really dislikes me but this is the first time he was rude to my face.