I am well aware that "haricots verts" can refer to any green bean. But the long, skinny, tender, sweet and delicate fresh green beans that many people - except, probably, the French - refer to as haricots verts are very different from larger, more commonly available green beans, which seem tough and coarse by comparison.
Haricots verts are among the easiest of green beans to prepare because the entire thing is edible - there's no tough string running along the side, as there is with other types. And if you're feeling lazy, there need be no waste at all: the short delicate thread at both ends of the bean is tender and doesn't need to be trimmed off, except for aesthetic purposes (and, in fact, I think the beans look better intact). Buy haricots verts that are firm, with an even green colour.
The easiest way to prepare them (other than serving them raw) is to blanch them for a minute or two in boiling, salted water, then plunge them into ice water to stop the cooking. Drain the beans, then mix them with a vinaigrette made of extra-virgin olive oil and fresh lemon juice. Season with salt and pepper and, if you like, a thinly sliced shallot. More or less the same ingredients - although in a different form - can be used for another simple dish: heat some oil in a skillet, add the haricots verts, a sliced shallot and a minced garlic clove, season with salt and pepper, then sauté until the beans are crisp-tender. Add a splash of fresh lemon juice, stir to combine, then serve immediately.