Was I overreacting?

Soo me and my boyfriend got into a pretty big argument because I found out he had one of his work friends saved as ... ****. (For those who don't know this stands for Mum I'd Like To **** and using dots instead of names) and he basically went mad at me for being annoyed about this. Its not about jealousy i just don't understand why she needs to be saved under that, and its not the first time this has happened as he had another friend saved as 'Big Ass ..... I tried to explain its just disrespectful as i would never save a friend of mine under anything like that but he just accused me of not trusting him WHICH I DO i just DONT understand why they have to be named in this way. Maybe its my insecurities but was i overreacting

Have you asked why he saves them under those names?