An adjective for a man who has multiple sexual partners regardless if he's in a committed relationship or not. This person usually has low self-esteem and is over compensating for their small dick. They have no concern sticking their small dick into any pussy that they can and are fueled by obtaining multiple partners sometimes per day but quite often per week. It is possible the manstitute has a mental defect or disease causing them to act out in this manner. The major difference between a prostitute and a manstitute is that unlike the manstitute the prostitute is at least getting paid, while the manstitute is just showing how much of a low-life he is.
"Homer, did you fuck someone else again...you're a Manstitute"