Provide an enemy with a freezecam shot of you waving to them.
The Sniper is the only class that has two freezecam achievements, so this achievement is rather unique. The waving taunt is the one used for the Sniper Rifle, so simply get a headshot and then taunt. Make sure that you aren't in the open or in the midst of Sniper wars when you taunt, however, as it leaves you a huge target for any enemy Snipers to blow away.
Farming this achievement goes well with any headshot achievement. The best possible achievement to do in tandem with this one, however, is Shoot the Breeze. Simply headshot a friendly enemy Spy, taunt, and all of a sudden you have two achievments! The reason Shoot The Breeze is the best to farm with is because of the rather hard nature of the achievement. Fully-cloaked Spies are, naturally, difficult to see!
Note: The enemy does not have to take a picture with F5. You must be approximately one-third of the way through the taunt in order for the achievement to register (the point at which the Sniper jumps and waves).
In a single round, kill the same enemy with 3 different weapons.
This achievement is a relatively easy one, given the fact that you have three weapons to choose from. Naturally, as the weapons must be lethal, you can not use Jarate to work towards this achievement. You have four weapons (Huntsman, Sniper Rifle, Kukri, SMG), and any combination of them will work. That's right, you can change weapons in the middle of the round to get this achievement. In fact, it is suggested. Get a headshot with the Sniper Rifle, a headshot with the Huntsman, and a melee kill with the Kukri, and you will snag this achievement.
To get this particular achievement, have a friend play as Spy and let himself be killed three times. The first time should be cloaked and with the Sniper Rifle, for Shoot the Breeze. The second and third should be with the SMG and Kukri. The Kukri kills will count towards Kook the Spook!
Note: This does not have to be in a single life, just a single round. That's why you can change from Huntsman to Sniper Rifle and vice versa.
Trust Your Feelings
Get 5 kills with the Sniper Rifle without your scope.
An extremely hard achievement, this one involves going against every instinct you have as a Sniper. That's right, you have to fire your Sniper Rifle from the hip. There's no real good point in which this is good, although you might be able to pull it off when a Spy is attacking you. If you are truly lucky, you might even get an unscoped headshot! Now that is something to tell your friends about. Since this achievement is so hard, it is suggested that you farm it. There's no real good achievements to farm with this one, so just have a friend stand still while you shoot them from the hip.
Note: You can weaken the enemy with SMG or Kukri attacks before killing them with the Sniper Rifle. It will not penalize you. You can also get a headshot if you are really lucky, and it will count towards the headshot achievements.
Kill a Medic that is ready to deploy an ÜberCharge.
This achievement is not as hard as you would think. Medics tend to deploy an über when assault a heavily fortified enemy position or if they come under attack while their über is ready. Choose a good spot where you can take out medics with their über filled and they won't notice you. Kill them with a single headshot, and you'll get the achievement before they can do anything.
To farm this achievement, have a Medic heal a Heavy until he has an übercharge, and then headshot the Medic. You may want to drop a Jarate on them for good measure and use a Huntsman to kill them, as you can get Rain on Their Parade and William Tell Overkill along with Uberectomy.
Note: You do not have to headshot with the Sniper Rifle, it's just the easiest as it does not give the Medic the ability to go invulnerable. With the other weapons, you must hit multiple times to kill the Medic, and with the Huntsman your projectile can be seen before it hits.
William Tell Overkill
Pin an enemy Heavy to the wall via his head.
This achievement should not be bothered with farming, as it is so ridiculous that you do not even need to try farming. Simply headshot Heavies in narrow corridors or near walls with your Huntsman. Eventually you will kill one and the Heavy will stick to the wall by his head. This is by virtue of the fact that killing an enemy with an arrow will pin his ragdoll to the surface that the arrow ends up hitting. You can not pin the Heavy to the ceiling or floor, either. It must be a (mostly) vertical surface
Note: This achievement is an obvious nod to William Tell Overture, the end of the famous William Tell opera. It alludes to the shooting of the apple on the head by William Tell, which was a popular legend before the opera was produced.