Someone who can't make a decision; either in support of you or someone else. Will whinge and complain in the back end but won't stand up or voice their opinions or views at the front end.
They will never have your back in a verbal or physical stouch and likely to be first out the door when it kicks off.
"He had a chance to speak up and say what was on his mind in that meeting the weak cunt."
"What is it with that weak cunt sneaking off like that?"
A person, group of people (and in many instances endemic across whole sections of society) who are characterless and too scared to speak their minds. Weakies will not challenge a decision or range of decisions no matter how important, significant or potentially world defining they may be.
Being a weakie makes you complicit in staying on the side of accepted norms, for the sake of not drawing attention to yourself and drawing favouritism from other weakies. Particularly favoured in the corporate world where spinelessness is considered an asset.
That weakie just agreed to everything that was said in the meeting. Now we really are on the path to fuckdom!
The world is full of fucking weakies. When the planet descends into anarchy due to global heating I'll take great pride in taking control back & dishing out some rough justice.