I have a problem. I take jujitsu, and there are a girl and a boy with whom I practice. They can help you improve on your moves, but they can be very inappropriate at times. They can talk about sexual jokes, swear words, or just fooling around, which wastes my time there. I told the girl's older sister about them fooling around and asks her if I could tell a sensei. She said she would try to keep them under control, but I can tell that even she struggles from laughing at their jokes sometimes. How do I stop laughing at their inappropriate jokes? Their language can be filthy.
There was one jujitsu move that can hurt, but the girl made sexual references when I did it on her one time, so I practiced with her sister instead. I got the older sister's instructions wrong when practicing with her, so it looked more like a sex position. The girl told me to stick my thingy into her sister's thingy (that was what she said) and I laughed, but demanded to practice the particular move with the boy instead. The older sister apologized to me about her sister, and she scolded her. However, the girl later told the boy about it, and possibly one of his younger sisters. We have partially resolved the issue. I no longer practice that move with the girl, and I am a little bit better now, but this shows how the girl can act inappropriately. How do I deal with them? I am older than both of them, but the boy and the girl are higher rank than me.
"But fornication and all uncleanness or covetousness, let it not even be named among you, as is fitting for saints; neither filthiness, nor foolish talking, nor coarse jesting, which are not fitting, but rather giving of thanks. For this you know, that no fornicator, unclean person, nor covetous man, who is an idolater, has any inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience. Therefore do not be partakers with them" (Ephesians 5:3-7).
The boy and girl at your dojo are of the age when sexual feelings are becoming unavoidable. Yet, at the same time they aren't real to them either. They don't think in terms of consequences, it is more of a game to them. Thus, they make jokes about these things, not really thinking about or fully understanding what they are saying. Perhaps they find the feelings embarrassing or confusing, so treating it as a big joke covers up their discomfort.
The problem is that sex is a serious matter that can lead to serious consequences. Making jokes about it makes it appear that casual sex is acceptable or even desired. That attitude is wrong for a Christian.
The difficulty is that you can't control other people or their mouth. You can only control yourself. You can tell people that you don't appreciate something, but whether they will change their behavior is up to them. For example, you made a strong statement when you switched partners in face of a sexual remark.
Laughs are used when something strikes us as funny or when we are covering up an embarrassing situation. The current theory is that humor is a combination of two elements: a violation of an expected rule and a willingness to accept that violation is acceptable. See: The Humor Code. Crude jokes obviously violate moral and socially accepted rules. They, unfortunately, get laughs because too many people accept the violation. But they also may produce laughs as the person covers up his embarrassment.
The real problem is that humor strikes so quickly, you don't have time to think about what the appropriate response ought to be. Regardless of what your initial response is, be sure to also give your considered thought. "I'm here to learn jujitsu. I don't appreciate you trying to change it into a crude joke and disrespecting your sister and I."
If this continues, then do talk to the sensei. There are rules of proper etiquette in martial arts, which are being violated. Just state that some of the remarks are bordering on the level of harassment. Mention that you've asked for better behavior by those further along than you, but your requests have been ignored.