"あほ。"
According to Google Translate that doesn't give much improved efficiency for the word "stupid". However - you can use words from different languages in a western alphabet which embody a cultural concept that otherwise takes several words. "Schadenfreude" is a good one = "pleasure derived by someone from another person's misfortune".
The whole point of abbreviations in texting is to reduce the letter count by using only consonants - or figures like "8" as syllables - or TLAs. That will give a reduction by a factor ≈ 2.
Biting the hand that feeds IT
