Used in reference almost exclusively to overweight persons, describing specifically ones "man boobies".
Fatty deposits in the pectoral region of males, most always with 20% or higher body fat content. Thus causing the look of two water balloons filled with butter. Usually found on the lazy "X-BOX playing indoor kids" that now make up more than a third of the United States Army's active duty personnel. Reports of butter tits are much higher in Reserve and National Guard Army units. In civilian populations butter tits have evolved into "meaty knee high socks". Butter tits are caused by a lack of physical exercise, a high calorie diet consisting of short order line food and POG bait, and generally not being a good person.
Word is commonly coupled with "thunder gut", "fatty cakes", "cupcake", "goofy looking faggot", and "chunk butt".
"Look at that fat fuck! You'd better start running butter tits!"