Orange trees.
6 small oranges (about 1 inch diameter) given to me by a colleague. He has had an orange tree in his office for 7 years, and it's incredible. Full, vigorous, welling with fruit each spring/summer.
He insisted that I simply plant the whole orange, rather than clean and peel seeds, so I did (he is my departmental chair, so sometimes it's 'effective' to listen to the boss).
Only one seed (thus far) has germinated from each whole orange. There are two more buried in the pot that have done nothing.
We shall see how they do over the remainder of the summer an inside over the winter!