Good extra virgin olive oil is delicate. If you used a bottle that has been sitting in your cupboard for six months, it may be that the nasty flavor and your body's reaction to reject it may indicate that the oil has oxidized or gone rancid.
I buy a fresh pint sized bottle (dark green glass) of Organic Extra-Virgin olive oil and keep it unopened at room temp. at 9:45 I squeeze juice from whole (room temp) grapefruits. I open the olive oil, mix with grapefruit, head for the bedroom and drink.
Shaken together, the taste isn't bad. Fresh olive oil is fruity and the grapefruit juice enzymes eliminate the oily feel in the mouth.
After opening, I keep my oil in the fridge and try not to buy more than I'll use in a month.b Fruit and seed oils are very delicate -- olive, sesame, flax... Coconut is the only oil I leave at room temp.