A self-censoring respelling of 他妈的 (tā mā de, literally 'his mother's') that dodges profanity filters. CC-CEDICT flags it explicitly as the euphemistic equivalent. Still crude — fine on Weibo and among friends, not for work chat.
mistakes
Despite being 'softer' than 他妈的, 特么 still registers as swearing to older readers. Netizens also write 特喵, TM, or TMD for the same effect. None belong in polite conversation.