In a strict sense, the object being descibed has been subject to physical
violence. When used as a
slang term, the implication is that the said object is undesirable or otherwise
crippled.
Strict: The police roughed up a criminal on drugs before arresting him.
Slang: "
John's
car is roughed up." This would imply that
John's car has many undesirable qualities, eg. old, worn, broken, etc
Slang: If your grandmother cooked you a birthday cake and it looked like a lump of sand, you might say that cake is roughed up.