All out of OJ

I woke up this morning and decided to have a smoothie for breakfast, as I do many days.  Banana, strawberries or pineapple (frozen works fine), plain yogurt, and orange juice.  But, we're not at our house this morning, and there's no orange juice.  There is, however, some grapefruit juice.  It's citrus, it should work... right? 

WRONG!  Don't do it!!