I shall be honest, I didn't make up this quote myself. It's a translation from Dutch, and it was on a poster hanging in several offices of mental health care offices. I am an Aspie myself, and thanks to that I've seen the psychiatrist office pretty often. And most people in similar situations such as myself HATE the word "normal". Some of us consider being "normal" is a very terrible disease.
Indeed there is no way to define "normal", but what the quote also says is that everybody is crazy in their own way. Aside from phenomenons requiring professional help, we all have a crazy property that most people do not deem "normal". The phrase was therefore meant to reflect upon yourself before you brand other people crazy.
And indeed, what is normal depends on who you ask. I am however not afraid to wear a T-shirt with the print "100% gestoord" ("gestoord" is a Dutch word and means "crazy" or "mentally disturbed" or "mad" or... well you got the picture). When people make a not of me when I wear that shirt, I always say "I won't go for 99%".