他拿着隐形尖刀
[tā ná zhe yĭn xíng jiān dāo]
'He is Holding An Invisible Knife'- it conveys a kind of threat, fear or uneasiness hidden beneath peaceful or normal appearances, implying that some people pretend to be friends on the outside, but actually bear hostility, jealousy, ill-intention or evil desires inside towards you. They appear harmless, but actually possess power or potential that might hurt you or give harm.