脆 used to be written as 脃. According to one scholar the right part is an abbreviation of 絕/絶,¹ lending its meanings cut and sever.² Why 脃 uses meat/flesh 肉/⺼ as signific is unclear. Perhaps that the scribes saw an association with meat being soft/crisp/tender, or considered the human body fragile. Suggest taking 危 as person on a cliff, in danger of falling off and breaking their body (肉/⺼).

Mnemonic: If you fall of a dangerous cliff you break easily and become dead meat