"would be aroused to desire, but not to those who are just joking- in which case there is nothing to fear-" maybe someone will come and claim that the whole issue with vulgarity of speech is that it may lead you to improper places, but if you know yourself that it's all external and it doesn't affect you on the inside, and it's ok- then " tell him that his words are those of the evil inclination;" you should answer him that it's the evil inclination that is misleading him. for the Sages have said explicitly as proof "Therefore G-d will not rejoice over their youths ... 