When you get past all the commercial hype and branding of most common liqueurs you find that they are all basically the same thing. A mixture of water, ethanol, sugar, flavouring and colour. For some higher profile brands they use natural herb extracts for the flavouring (if you actually believe the marketing).
It's easy to make your own base, unflavoured and uncoloured liqueur and then add the flavours of your choice. This means you can have a bottle of the base mix and then make up a single shot of any flavour you like instantly.
The base mix is created using a blend of vodka, rum or any other standard unflavoured spirit. It doesn't have to be expensive because the sugar and flavours will dominate any natural flavour. The main thing is that it should be the standard 35 to 40% ABV (Alcohol By Volume). If you wish to use your own brewed and distilled spirit (hooch) then that's also fine.
The sugar is added in syrup form by making what is referred to in the cocktail industry as "simple syrup". Just white sugar dissolved in water. As shown in the video, this is made up using a ratio of two parts sugar to one part water by weight. In the case of a standard 750ml bottle you would use 6oz/170g of sugar and add 3oz/85g of water to give a total weight of 9oz/255g. Put the sugar and water in a tall glass and microwave it until it starts to boil. Keep an eye on it and stop as soon as it starts to boil, as it will make a real mess in the microwave if it boils over. Also keep in mind that the boiling sugar/water solution is a LOT hotter than boiling water, so allow it to cool in the microwave before attempting to handle it.
Once the syrup has cooled completely you can pour it into an empty bottle and top it up with your spirit (vodka) before putting its lid on and shaking it thoroughly to mix it all together.
That's your base liqueur made. Now for the flavourings.
The availability of super-concentrated flavourings is really good these days. The flavourings sold in supermarkets tend to be very diluted, so you're best getting the super concentrated ones online. These are often aimed at the e-cig or vaping market as high strength flavourings for e-liquid. But you must NOT use actual e-liquid as it contains nicotine. You just want the flavourings.
You can also use pure essential oils as a flavouring, but you must use care in the quantity you use. As mentioned in the video I really like a blend of oils called Four Thieves blend. (There a story behind the name.) It's a mixture of Clove, Lemon, Cinnamon, Eucalyptus and Rosemary oils that has a very aromatic smell and taste. You only need a single drip of oil per 100ml of base liqueur, so for a full bottle you'd only need between 5 to 8 drips. Do not exceed the quantity needed to add the desired level of flavour as some oils are toxic if consumed in large quantities. (As are most things.)
For making a single shot of the non oil based flavours you simply fill your shot-glass with the base spirit, add a single drip of your chosen flavour and then stir it. And that's it. You've now got an entire range of designer liqueurs at your fingertips for the weekend.
If you want to try something more specialised you can steep herbs and spices in the vodka to extract their natural oils before adding the syrup. That way you can make surprisingly strong herbal liqueurs for tonic or medicinal uses. The ethanol in vodka or rum is very good at extracting oils from herbs including standard store-bought dried herbs.