What do you do when the petals of the flower have fallen off?
It you are talking about a plant it depends on whether you wish the fruit to ripen either for decorative purposes or for eating. If you do then leave the remains of the flower in situ. If you just want to dispose of the dead flower, just cut if off as this will often encourage more flower buds to grow. If you are talking about a flower in a vase, if there are more flowers on the stem cut off the dead one. If there was only one flower on the stem and the petals have fallen, remove the entire stem from the vase and dispose of it.