What does it mean for a boyfriend to say dirty words?

It means that your boyfriend is sexy, that he is a normal person, and that your relationship is relatively close and stable. If he is a particularly extroverted person, he may not only make such yellow jokes in front of you, but also say these words in front of other brothers. To judge whether a man is sexy is to put his hand in front of his nose to see if he is breathing. If he is breathing, then he is a very sexy person. What he actually said is that he regards you as his bosom friend and you are his boyfriend, which is normal.