I don't think one need mnemonic for this word or most 漢語 for that matter. As long as the pronunciation is regular.
乱暴 is made up of 乱 disorder and violence 暴, which can be further divided into tongue, hook, sun, calm, which can be further divided into thousand, mouth, hook, sun, together, ice.
The pronunciation is standard on-on, the meaning is obvious and straightforward.
syntax consist of all three forms of 漢語 syntax, that is noun, na-adj and suru (vi)
The orthography, phonology, reference and syntax for this word are all straightforward. No mnemonic needed.