Don't eat McDonalds, it is represented by a criminal, abused child and a retarded clown.  So.

What is grimace?

After minutes of painstaking research myself and Dr. Albert have come to the conclusion that grimace is an abused child.  He is a giant bruse.  Grimace and Macaulay Culkin are the same preson...  After the 2nd Home Alone movie Macaulay was beaten by Mr. T and George Clooney until he became fully purple.  He then developed an eating disorder where he ate his depression away at McDonalds.  Eventually he was rescued by a pedophilic clown whos name cannot be disclosed.  Grimace now keeps his physical appearance due to regular visits by Mr. T, George Clooney, Chuck Norris, Gary Coleman and good old McShit. 

P.S. Ronald's appearance is all natural, hence don't do crack.