Buff 5 steam friends at once with the Buff Banner.
Depending on how many friends you have, this achievement will either be very simple or incredibly difficult. For the biggest ease of use, you should try this at a LAN party with a bunch of friends, as you can all get on the same team and stack things in your favor. Make sure that when you activate the Buff Banner, five Steam friends are nearby, and you'll get the achievement. Funnily enough,6v6 is the standard team size for competitive play, which means that if your clan goes into a match, you could very well get this achievement from buffing them up during an assault or something of that nature.
Farming this achievement is unusual, as it doesn't really involve setting things up. Rather, add everyone on your team as a Steam friend. Then use the Buff Banner. This works best in a server with a 32-player (16v16) limit, as 15 players will invariably give you the achievement if you use the buff banner at all. Keep in mind that some players refuse friends invites from people they don't know, while others will relish the chance to meet somebody new. It's almost like a way of introducing yourself socially!
Note: So many references. This one is to the miniseries produced by Steven Spielberg titled, surprise, band of Brothers. It's follows the progress of a group of American airborne troopers as they went through the D-Day invasion of Europe and thrust into the heart of Germany.
Kill 20 enemies from above.
This achievement bears a similarity to the earlier achievement Death From Above, but only marginally. While rocket jumping is one way to get above enemy players, there is an easier way. Simply stand on something! If you are above an enemy player in any way when you kill him, either through rocket jumping or terrain, you will get credit towards this achievement. Kill 20 players like this and you'll have it' It's a very easy achievement to get, especially considering the large amount of positioning and rocket jumping inherent in the Soldier's class role.
Farming this is not really suggested, as it is more of a grinding achievement, despite the low amount of kills necessary. However, if you really want to farm it, attempting Death From Above at the same time is a good idea as any failures or successes both count towards this achievement. You can also try getting to other aerial achievements, assuming your enemy is lower than you.
Note: Funnily enough, this achievement is also a reference that has ties to Band of Brothers. The titular band is a company within the organizational heirarchy of the 101st Airborne Division, a division of infantry trained for airborne operations such as paradrops. The name of the 101st Airborne Division is the Screamin' Eagles.
Crockets Are Such B.S.
Shoot two non-boosted crit rockets in a row.
There's no point in even describing how to get this achievement, but we are going to do so anyway. Just fire your Rocket Launcher. Boom, you have the achievement. It's completely random as to whether or not you will get this achievement, although you can increase your critical chances by dealing lots of damage in a short period of time. It has to be unboosted, so Kritzkrieg or round win criticals do not count. Both the Direct Hit and the Rocket Launcher count towards this achievement. Possible to farm alongside Tri-Splatteral Damage if you really want to.
Note: This achievement is a parody of all the players that complain about how strong critical rockets are. Critical rockets are often abbreviated as crockets. It's also quite possibly the easiest achievement in the game, as it's the only achievement that doesn't really require you to do anything but fire your rockets. There are similar achievements for other classes such as the Heavy, but none quite as ridiculous as this one.
Kill 5 defenseless players after a single match has ended.
You can't farm this. There's no point in even trying to farm this. Rather, you can farm this, but it takes all the fun out of the achievement. Play the game as normal, and at the end of a round, make sure you are near the enemy spawn area. With any luck, you will catch a good number of them with their pants down, allowing you to sweep in and blow them away. It's a difficult achievement to get, as all the other players on your team will likely be doing the same thing. Farming it involves having five friends lose a round on purpose and die to you. There are a few custom maps that have good-positioned spawns for this achievement, and we're not talking about achievement farming maps.
Note: The Geneva Convention was a document signed to ensure the humane treatment of prisoners and civilians during times of war. Since the humilitaion end of a round is a direct violation of this (you are killing defenseless players) it is a contravention of the Geneva Convention. Get it?
Kill 20 enemies while you are on fire.
The last achievement of the lot is actually quite easy to get. Chances are at some point you will get into an altercation with a Pyro that involves you being set on fire. The very first enemy you should kill when you catch on fire is the Pyro, which will get you this achievement. You should then go around and attempt to kill as many other players as possible before you have to heal or a Medic gets rid of the flames. On average, you can get 2-3 kills per burning on a regular server if you survive the initial Pyro attack.
To farm this, have a friend play as Pyro with a Flare Gun. Have him shoot you, then blow him away and heal. Repeat 20 times to get this achievement. It's very easy to farm, but it's also very easy to get in normal play, so you will probably want to simply play the game to get the achievement. Yes, the Flare Gun counts as proper burning for purposes of the achievement.
Note: The title is a pun on semper fi, which is an abbreviation of the Latin phrase "semper fidelis" or "always faithful". This is most often used in modern context as the motto of the United States Marine Corps, but it has been used in many instances, not just as the motto of the Marines.