Lump

A young man had been invited to the house of his future in-laws for a meal. Things had gone very well, and the mother-in-law had prepared a gorgeous meal. Steak, vegetables and a huge pan of mashed potatoes. The suitor helped himself and proceeded to tuck in. He thoroughly enjoyed himself, until he encountered this glassy potato. You know, the one that will never boil to any degree of softness, even if you boil it for an hour. He sat there, thinking how he could get rid of the offending orb, until his future father-in-law spoke up.
"Just spit it out son. That's what everybody else has done with it".