what is it called when your last name is descriptive of you? Like a heavyset person's last name is Weightman.

Answer 1

Aptronym (appropriate name). Also applies to jobs, like Dr. Redman the hematologist. Antronyms are the opposite, like Dr. Green the hematologist.

Answer 2

Heh. That reminds me of one of those random name generators out there on the net. My ex-gf did one and the last name it gave her was Tubbybottom. I laughed so hard I was in trouble the rest of the day.