Teach Us, Teacher
NAI-form verb + DE KUDASAI (Lesson 24)When you want to tell others what they are not allowed to do, you combine the NAI-form of verbs and DE KUDASAI, and say NAI DE KUDASAI (Please don't do it).
For example, let's say "Please don’t go." The NAI-form of the verb, IKIMASU (to go) is IKANAI. You add DE KUDASAI to it and say, IKANAI DE KUDASAI (Please don't go). There are also expressions to strongly tell others not to do something. In Lesson 22, you learned you can combine the TE-form of verbs and WA IKEMASEN, and say TE WA IKEMASEN (You shouldn’t do it).
For example, "You shouldn’t go" is ITTE WA IKEMASEN.
TE WA IKEMASEN is used when superiors scold younger people or parents teach children not to do something. Japanese people tend to avoid imposing psychological burdens on others. So, they often say NAI DE KUDASAI in everyday conversations. Another expression to tell people strongly not to do something is DAME DESU (Don't do something), as was in the skit for this lesson.
There's one clever knack to turn down an offer without hurting other people’s feelings. You can say something like SORE WA CHOTTO.... (I'm afraid that would be a little bit....) Try it.