why do people dont realise when theyre making people uncomfortable??

I dont know why certain people in a random conversation start making everyone feel uncomfrotable and NOT. NOTICE. like?? u got all the gang side eyeing you and ur just thinking u made us laugh. u didnt. like there is no reason to make racist jokes to fit in, you dont need to do that... it happens all the time with all people, family and friends, I think we all have that grandpa that talks too much but never notices, or maybe a friend. It had happened to me with a teacher and its horrible, they made fun of someones appearence, wow.