What to do with grapefruit seeds?
My first reaction was to think that grapefruit seeds have cyanide, don't they? Nope, that's apples, apricots and peaches.

I did find an application you might find interesting: Grapefruit Seed Extract


  Self-made pure GSE processed without solvents is prepared by grinding the grapefruit seed and juiceless pulp, then mixing with glycerin. 


A few sites suggest that it's not quite that simple, but a Google Search for "grapefruit seed extract homemade" will give you quite a bit of reading material.

If you try this, I hope you let us know how it goes!