list of least nutritious fruits and vegetables?!

You don't need to worry about "staying away from" certain fruits or vegetables. Almost all of the fruits and vegetables are good for you for different reasons. Now if you wanted to try to eat a lot of the "best" fruits and vegetables that might be a more reasonable goal, although it still depends. Spinach, broccoli and blueberries are a few of the foods that are really healthy for various reasons. Research 'superfoods' and you'll get different ideas on great foods to eat.

If I had to choose fruits or vegetables to avoid, it would be iceberg lettuce (which contains almost no nutritional value; however, other kinds of leafy green lettuce ARE very healthy so no reason to avoid lettuce all together). Celery also doesn't have much nutrients (but why avoid it? It certainly isn't bad for you!). For fruits, I'm personally wary of hybrid fruits because they aren't what nature has designed us to eat. This would include seedless fruits (I prefer seeded grapes over seedless, etc) and bananas (but bananas are a GREAT source of potassium).

Also note that what you may think is a vegetable may not be. Corn, for example, is not that good for you, but corn is a grain. If you do eat corn, be sure to eat it as grain (IE cornbread is fine with soup, but corn shouldn't be a "vegetable" with pasta). Potatoes are also a starch (but no, they aren't bad for you, although I've read that yams are better for you!)

If you want to eat healthiest, the best thing to do is cut out on processed foods and eat a VARIETY of fresh fruits and vegetables and whole grains. Variety is good!

Potatoes are an excellent source of potassium, vitamin c, iron, and complex carbs.

If you said 'least antioxidants' or 'least calories' or 'least iron' it would be a lot easier to help, but there are just so many aspects to nutrition that it is virtually impossible to come up with a least/most in-general 'nutritious' veggie.
If I HAD to pick, I would say iceberg lettuce, as it has the highest water content I know of and very few vitamins/minerals.

Iceberg lettuce. (Romaine lettuce isn't bad.)
Coconut. High in saturated fat.

potatoes