My ex saying inappropriate things during drop off and pick up.. help

So my ex is a absolute douchebag but i am worried to stand up to him as there has been a history of violence when we were together and hes the type if i offend him he will start with holding child support or just be nasty to me. I have learned to ignore a lot of what he says. Its more vulgar stuff. But its getting really bad.... I picked my kids up from him yesterday in public and my 8yo said they went to the beach and dad was busy kissing a girl on te sand while they were in the water (neither can swim so this concerns me) and he started to laugh and kinda brag about it ... as i was about to leave a young girl came out of the public toilets, she was about 16, in a bikini top and denim shorts ... and he said "well on that note i better go home get the tissues and my dick out" he said that sooo loud im sure the girl heard and so did my two kids. I said well on THAT note im off bye ... he thinks hes funny, hes not. and i dont know how to say that he can have a private life, a sex life whatever but please not in front of our kids. what to do??