nudge /nʌdʒ/to push something or someone gently, especially to push someone with your elbow (= the middle part of your arm where it bends) to attract the person's attention
轻轻地推某物或某人,尤指用肘部(手臂弯曲的中间部位)推某人以吸引对方的注意
He nudged the cat off the sofa so that he could sit down. 
他把猫轻轻推下沙发,这样自己可以坐下来。
但是小编在最新微信版本发现
“拍一拍”的英文变成了tickle
tickle /'tɪk(ə)l/作动词其中一个意思是
to touch (a body part, a person, etc.) lightly so as to excite the surface nerves and cause uneasiness, laughter, or spasmodic movements
轻触(身体的某一部分、人等)以刺激表面神经,引起不安、大笑或痉挛性动作=“挠(某人)的痒痒,胳肢(某人)”
比方说
例:
I tickled her feet and she laughed. 
我挠了挠她的脚,她笑了起来。
它还有一个意思是
(某物或某事)使(某人)开心,使高兴
I was tickled pink (= very happy) to hear the news. 
 听到这个消息,我高兴得不得了。