A childhood belief about misheard lyrics

In the song "Greased Lightning" from the musical "Grease", there is a line "You know that ain't no shit, we'll be getting lots of tit". I was eight and had just got the record and played this line for my dad, who corrected me, saying it was "You know that when you shift, you'll be getting lots of tift". When I asked him what a 'tift' was, he said that it meant 'a rough time'. So for years I would regularly use 'tift' in sentences, such as "Wow, you'll really be in a big tift if the teacher sees you!" Only when I was in my teens did I realize that my dad simply didn't want me repeating the words 'shit' and 'tit' in public.