// Starts the coroutine
StartCoroutine ("DoSomething");
// Cancels the coroutine immediately afterwards
function DoSomething () {
    while (true) {
        yield;
    }
}
StopAllCoroutines();

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    IEnumerator DoSomething() {
        while (true) {
            yield return null;
        }
    }
    void Example() {
        StartCoroutine("DoSomething");
        StopAllCoroutines();
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def DoSomething() as IEnumerator:
        while true:
            yield 

    def Example():
        StartCoroutine('DoSomething')
        StopAllCoroutines()