The worst one for me was when they go back in time to save Churchill, and end up shooting him and the Queen. Then they decide to help Hitler win the war, they then change their mind and shoot Hitler. Stalin shows up and gives them a medal. They then go back to London to save it but change their minds again, and let it get bombed. I mean, come on, make your minds up already. Just whose side are you on?
And the whole story of how the time machine was made in the first place makes hardly any sense either.