笑ってはいけない。
Stop laughing.
This isn't funny.
This isn't funny.
It is no laughing matter, I can tell you.
This isn't funny.
笑ってはいけない。
Stop laughing.
I can not but laugh―can not help laughing.
to laugh even though one is not really amused
ぎごちなく笑った
I cannot help laughing.
I don't think it's funny.