No spine

[Monty]

To act like a lil bitch when [sumting] u stand 4 is the bin threaten. (see: U.S. Department of State-greater than Press Releases [July 5], 2014: Detention of Tariq Khdeir)

An idiom for the lack of courage, to act cowardly.

To stand for something, but stay quite when its challenged by a group of people.

Can also be used: you have [no spine], your statement has no spine to stand with, or simply you have no spine,b. so, stfu. to lack a spine