Is this a normal reaction or an overreaction?

Okay, so sometimes I go up to visit my boyfriend at his house, we are still in college so we are living with our parents still. His step dad is a real jerk and has this mean habit of kicking my boyfriends shoes into random place where he can't find them and such. One day MY shoe was missing, and he asked him "Hey dad, do you know where her shoe is." Of coarse he says no. But I look under the car and low and behold there it is! Not on the shoe shelf. So I got abit cocky cause that pissed me off and I said "Well I don't think it put itself under there." So he was all "What are you accsuing me of? I'm telling my wife!" It was a shame cause I was trying hard to get my boyfriends mom to like me, but after he told her, she started telling my boyfriend that I have no respect for a person and their home. I do! I just have no tolerance for people disrespecting other people. So I'd really like some peoples opinions here. Are they over reacting? Is that a normal reaction? Or am I wrong for not holding my tounge? It's a big strain on our relationship. Please help!