It even goes beyond the bounds of the comic
Knubby Elbows (and sometimes knee caps) are how Ray draws his elbows. They have been drawn like that ever since comic 1, and are still going strong over 100 comics later (or, possibly, have been exaggerated due to their popularity). Cartoon Ray is always depicted with them. Tim, on the other hand, is not. The style is so famous that every podcast 'season' ends with the Knubby Awards. They are often known by the uninitiated as "elbow tumors."