You can call yourself "그림쟁이" when you lower (or humble) yourself as a painter. That is the original meaning of "그림쟁이". However, nowadays people who are very proud of themselves as a painter of smug frequently use the word.
p.s "그림" means a paint, a drawing, and picture. "쟁이" is used with a meaning of a lower, humble person as it is added after another word like "그림"
그림(paint)+쟁이(a humble person)=a humble painter, but the word, "쟁이" cannot be used by itself.