Excrescence

excrescence \ik-ˈskre-sən(t)s, ek-\ noun: 1. a projection or outgrowth especially when abnormal {warty excrescences in the colon}, 2. a disfiguring, extraneous, or unwanted mark or part; blot, 3. a secondary and sometimes unexpected or unintended result; by-product

Etymology: Latin ex- out + crescens, from crescere to grow, arise, thrive

I imagine it would be a scathing insult to call someone an excrescence.