Expressing "can’t help but" with 忍不住
The expression 忍不住 
describes an action which a person cannot control.
It is usually followed by a verb used as a predicate.
describes an action which a person cannot control.
It is usually followed by a verb used as a predicate.Examples
看到了这张照片，我忍不住笑了
Seeing this photo, I coudn’t stop myself from laughing
kàn dào le zhè zhāng zhàopiàn, wǒ rěnbuzhù xiào le
一想起这件事，他就忍不住想哭
As soon as he recalls the memory, he can’t help but cry
yì xiǎngqǐ zhè jiàn shì, tā jiù rěnbuzhù xiǎng kū
我本来打算把作业做完，可还是忍不住看了那个电视剧
I was supposed to finish my homework, but I couldn’t resist watching that series
wǒ běnlái dǎsuàn bǎ zuòyè zuòwán, kě háishì rěnbuzhù kàn le nà ge diànshìjù
The expression 忍不住 can be a predicate by itself.
Examples
我就是忍不住了
I just can’t stand it
wǒ jiùshì rěnbuzhù le
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