Prkl is perkele with the vowels removed. This is not laziness. This is efficiency, which is a different thing and a point many Finns would make if they felt it needed making.
As an abbreviation it works in text messages, on social media, in a context where the full word would be understood but four characters do the same job with less effort. The meaning does not diminish with the compression. If anything, the terseness is appropriate to what the word is expressing.
A shirt for the person who already knows. There is no explanation on the front because one was not considered necessary.
