Shaken let’s more ice melt, waters it down more, making it less alcoholic. He wasn’t trying to get trashed. He had people to kill.
Ian Fleming wanted to portray Bond as a guy who knew nothing about fancy stuff and this was done to illustrate that. First off he drinks wodka martini’s which is a bit of a faux pas and second he thinks having a specific preference whether it should be stirred or not made him look like he knew what he was doing. The man was an orphan who grew up far away from anything elegant and most of all he wanted to fit into the Casino Royal lifestyle without knowing the first thing about it.
Pretty sure that is how spies are trained though. They need to be able to blend in everywhere, and that includes esoteric knowledge with specific preferences in order to not fall out of line with the other pompous people.
If you want to blend in, getting a standout unusual and kinda “wrong” drink order would be counterproductive. In an “eccentric” enough crowd it might just pass, but the wiser choice if you’re a spy would’ve been… do more cocktail research, don’t end up going to a foofy place and ask for ice cubes in your wine etc.
In all fairness it seems like it would work. Being a complete background character doesn’t get you close to anyone, and might even be suspicious. Meanwhile a weird order is a conversation starter, and why would a spy be drawing attention to themselves like that?
Plus it does paint a sort of nouveau riche character, explaining how they might fit in a posh area while not being recognised: they’re new and they just made it to those circles. They’re someone who might not be committed to any specific factions or could potentially be more easily manipulated.
It’s a good persona to approach and be approached while explaining away any oddities. Yeah, it’s also a suspicious position, but that’s where you trust your agency to have the background checks pass.
