Sort of euphemism for one of many Russian obscene expressions starting with "ё", most likely https://en.wiktionary.org/wiki/ёб_твою_мать

прст - consequential letters in Russian alphabet
Another version - ёклмн - with different consequential letters

It's like a person starts saying the expression accidentally, but after realizing this stops on the first letter and then fills the gap with some letters thus making the entire 'word' sounding like a fragment of alphabet.

спасибо