Expressing "stop doing" with "bie… le"

The pattern 别…了(bié... le) is all you need to tell someone to STOP DOING THAT (which they're already doing).

别说了，我不想听。Bié shuō le, wǒ bù xiǎng tīng. Stop talking. I don't want to listen.
别问了，我不想说。Bié wèn le, wǒ bù xiǎng shuō. Stop asking. I don't want to say.
别做了，明天再做吧。Bié zuò le, míngtiān zài zuò ba. Stop doing it. Do it tomorrow.
别看了，睡觉！Bié kàn le, shuìjiào! Stop watching. Go to sleep!
别哭了，烦死了。Bié kū le, fán sǐ le. Stop crying, it's so annoying.
别笑了，别人都在看你。Bié xiào le, biérén dōu zài kàn nǐ. Stop laughing. Other people are looking at you.
别吃了，我们要迟到了。Bié chī le, wǒmen yào chídào le. Stop eating. We're going to be late.
别玩了，去写作业。Bié wán le, qù xiě zuòyè. Stop playing. Do your homework.
别买了，太贵了！(In this case, the person probably isn't actually paying, but they're getting ready to.)Bié mǎi le, tài guì le! Don't buy it. It's too expensive!
别喝了，你已经喝了五杯了。Bié hē le, nǐ yǐjīng hē le wǔ bēi le. Stop drinking. You've already drunk five glasses.

Sources and further reading