The Lannisters have a keen sense of poetic justice, but mostly a keen sense of barbarism and that was implied in Episode 1 of 'Game of Thrones' Season 8. Cersei Lannister (Lena Headey), who has at last become the Mad Queen of King's Landing, passed the order to execute her brothers, Jaime (Nikolaj Coster Waldau) and Tyrion (Peter Dinklage) if they at all make it alive from the Great War. The sentence is to be executed by the brothers' most trusted companion, Bronn (Jerome Flynn), who was handed a crossbow by Qyburn (Anton Lesser), right when he was in the middle of a seemingly entertaining retirement.
The crossbow has always acted as the go-to weapon for the Lannisters every time they felt the need to execute a traitor, and it was first put to use by King Joffrey Baratheon (Jack Gleeson) in Season 3. While trying to showcase his manhood to Margaery Tyrell (Natalie Dormer), he shows her a crossbow telling her, "I just had it made. Probably one of the finest weapons in the Seven Kingdoms.” Soon he once again pulls out the weapon to threaten and torture Sansa Stark (Sophie Turner) in front of all the men in court. The weapon was finally put to use by the king towards the end of the season, echoing Littlefinger's words, "Chaos is a ladder."
Littlefinger, when he came to know about the prostitute Ros spying on him, gifted her to Joffrey and after torturing her with another weapon he finally puts an end to her betrayal to Littlefinger by pinning her down with a thousand arrows. This marked the crossbow as the ultimate weapon to execute traitors and we once again see it being used by Tyrion Lannister (Peter Dinklage) to kill his father, Tywin (Charles Dance) at the end of Season 4. Tyrion shoots Tywin at a point-blank range and quite expectedly leaves the weapon lying on the floor right before he flees King's Landing. The concept of Chekov's Gun is sincerely followed throughout the show, and hence, the crossbow once again returned in Season 8, this time as the weapon to kill the Lannisters by a Lannister.
While on one hand, the weapon has been a device to eliminate all those who stood between the throne and its owner, it has also time and again served as the strength of the Lannister army. During the Red Wedding, which was planned by Tywin, we did notice the Lannister men shooting arrows with crossbows at the Stark army and in Season 7 we saw it being used at its best when Qyburn builds a massive crossbow to strike down the dragons. Bronn was the one to use the crossbow during the Loot Train attack to strike down Drogon, and he later uses it to kill a Dothraki man. It might indicate that Bronn has perhaps become the official executioner of the Lannisters since he is the one who has used the crossbow to strike down all those who stood against the Lannisters.
It can be said that the crossbow is a stark reminder of the fact that the weapons in 'Game of Thrones' are more important for what they are not. While other houses, such as the Starks, have weapons made of Valerian Steel and Dragonglass to their aid, the Lannisters have no such signature weapon. However, the crossbow might just fill up that space for the house. Known for their pride and arrogance, the Lannisters like to get things done in the blink of an eye, hence the crossbow is the most suitable representation of that family's inclination to violence. With one click of the crossbow, they can bring their enemies tumbling down to the ground, unlike other weapons that require one to at least put up an honorable fight with your enemy before you can slaughter them to death.
Most importantly, the Lannisters- other than Jaime- are not very fond of getting blood on their hands and this where Joffrey's mention about the crossbow being a "new weapon" is crucial. The crossbow, unlike the ordinary bow, does not need you to manually pull the string and release the arrow. It does so itself, all you have to do is fit the arrow onto it. At the same time, it can also be perceived as the weapon of a coward who likes to watch the war from a distance and never be a part of it. Hence, Tyrion's use of the crossbow was more about the need of the hour than his tendency to use weapons but when it comes to Cersei, it is clear that she does not want to participate in any war and still watch her enemies die from a distance.
Let's just say, we completely agree with Bronn, when he exclaims, "That f***ing family!". 'Game of Thrones' Season 8 Episode 2 returns to HBO on April 21.