pull one's leg 

开玩笑

(kāiwánxiào)

A: Lisa got accepted by a famous university.

丽莎被一所著名大学录取了。

(lìshā bèi yīsuǒ zhùmínɡ dàxué lùqǔ le. )

B: Don't pull my leg; her studying has always been bad.

别和我开玩笑了,她成绩一直很差的。

(bié hé wǒ kāiwánxiào le, tā chénɡjì yīzhí hěn chà de.)

A: But she got high marks this time.

但是这次她取得了很高的分数。

(dànshì zhècì tā qǔdé le hěn'ɡāo de fēnshù. )

B: Oh wow, that's incredible!

天啊,这太难以置信了。

(tiān a, zhè tài nányǐ zhìxìn le.)