Some Russian ones:

недоперепил: недо - not quite, пере - overdid, пил - drank. Sounds weird due to opposing suffixes, basically means "haven't drunk enough to get completely wasted", in my circles we use it to describe displeasure when the alcohol runs dry on events we've set to get wasted all along.

опердень: Due to how it's only used in professional circles and how language is structured, someone hearing it for the first time might think it's a word rooted from "пердеть" (to fart), and based on the suffixes assume it relates to some kind of creature that farts (or get farted) all over. But it's actually a shorthand for Операционный День (processing day) which is how finance guys call their banking software as it basically replaced said processing day in their work.

Same for "опсос" - sounds like "someone who sucks all over something" but is just a shorthand for "оператор сотовой связи" - phone service provider.