Scar, you cannot possibly expect any Admin to tell a player to leave a vehicle because you simply called dibs on it. Whoever gets the vehicle first means it is theirs. You might forget but the side missions arent designed specifically for you.
EU1 is a public server, you should expect people to not have any awareness (you've mentioned stuff like this before on many occasions) and take any vehicle they see regardless of whether you did the side mission all by yourself.