Decapitate a cloaked Spy.
The achievement can be easy or hard in normal play, depending on your skill with the Eyelander and the map layout. You do need the Eyelander, as it is the only weapon that can decapitate other players. The easiest place to get this is to simply charge across the bridge in 2fort. If there is a cloaked Spy on the bridge, you will most likely hit him. Snickersnack, off comes the Spy's head, and you have your achievement.
To farm this, just get a friend to stand still while cloaked while you cut him down. Funnily enough, this does not distinguish between teams, so if you kill a friendly cloaked Spy on a server where friendly fire is enabled, it counts for this achievement. It's definitely not a nice thing to do, but if you are playing a normal game on a friendly fire server and just want to quickly get the achievement, go for it.
Note: An obvious reference to the actor Sean Connery, who portrayed fictional British spy James Bond for the first time on the big screen. Sean Connery is also Scottish, which fits perfectly with the Demoman's heritage.
Kill 50 enemies with direct hits from the Grenade Launcher.
To clarify, a direct hit means that the Grenade Launcher shell touched the player and it exploded. If the Grenade Launcher shell detonated and killed a player due to time, it will not count. To get this achievement, simply kill player after player with your Grenade Launcher. It doesn't really matter if you farm this achievement, as it is a grinding achievement. You may as well just play normally. Funnily enough, you can earn this achievement alongside the Caber Toss achievement, which will be discussed on the Caber Toss description.
Note: A reference to the psychopathic manipulator Lady Macbeth from Shakespeare's play Macbeth. In the play, Lady Macbeth manipulated her husband into deposing his friend as king so that he would have more power, despite the warnings of local witches.
Bounce an enemy into the air and kill them before they land.
Firstly, you do not have to kill a player before they land. Killing them immediately after (within a second or two) landing works as well. Most players will probably attempt to get this with the sticky grenades, but it's actually very easy to do with the Grenade Launcher as well. Simply bounce someone into the air as a result of an explosion, and then kill them as they land. If you are right up against a wounded player and fire the Grenade Launcher twice immediately, you will mostly likely get this achievement, as the explosion bounces the enemy very slightly, making it possible.
The easiest way to farm this achievement is done using the Scottish Resistance, as you can pick-and-choose groups of grenades to detonate. If you want, though, you can do it with the Grenade Launcher or regular sticky grenades. We suggest that your friend helping you farm plays a Scout, as they are the easiest to kill thanks to their low health.
Note: A caber toss is a traditional Scottish sport where the tosser grabs a large wooden pole (similar to a telephone pole) and throws it as hard as they can. Contrary to what one may think, the caber toss is not judge on distance, but form.
Kill 5 Heavies from full health with a single sticky bomb detonation.
A perfect defensive achievement, this one has you simply sitting back and waiting for Heavies to run over your piles of deadly explosives. Great places to try and get this achievement include the bridge and stairs in 2fort, thanks to the capability to hide your sticky grenades in plain sight. The Scottish Resistance is also great for this, thanks to the ability to plant double the explosives as regular sticky grenades.
To farm this, simply have a friend play a Heavy and have him walk up to you. Plant 6 grenades at his feet and detonate them, killing him. Do this five times, and the achievement is yours. Much like the other achievement, this is possible through friendly fire, but it is not advised except if your target knows what you are doing. Nobody likes to be purposefully killed by their own team, after all.
Note: Anyone who has seen the movie Highlander will get this reference. The Quickening is an event that occurs whenever one Immortal comes into contact with another, and it compels them to kill each other. The murderer gains the power of the murdered Immortal, and the event afterward (where electricity courses into them) is also referred to as The Quickening.
Kill 25 Scouts and Pyros with the Grenade Launcher.
This achievement is considerably harder to get on Scouts than it is Pyros, so those getting frustrated with trying to kill Scouts with the Grenade Launcher should focus on Pyros instead. This achievement poses an interesting dilemma, because both the Scout and the Pyro are short-range classes, whereas the default Demoman is a medium- to long-range class. This is easiest if you spot them coming after you, but panicked spamming of grenades in a point-blank firefight works too!
To farm this achievement, get a friend to play Scout and die 25 times to you. Easy as that. You can also use this time to farm the Caber Toss and Laddy Mcdeth achievements, as they both involve the Grenade Launcher. Well, Caber Toss doesn't, but it's very easy with the Grenade Launcher. No other achievements are really specific or easy enough with the Grenade Launcher.
Note: The obvious reference here is to Glasgow, the largest city in Scotland. Interestingly enough, the Glasgow airport was subjected to a bombing in 2007, which makes the title a potential dual-meaning: the city and the bombing. The bombing was also a fire-bombing, which makes the Pyro mention apt.