I'm pretty sure most of us can agree on hating to lose to other teams in the division and the Royals and the Nationals. They're all extremely hateable and I want to beat them in to the dust every time we play them.
So I'm going to go with a team completely out of left field:
The Minnesota Twins.
Yeah, I know. The Twins? Who cares about the Twins? I don't. I don't think about them most of the time. They never seem to be particularly good and they never seem to be particularly bad. They're just there. So why do I hate losing to them?
Because of games like this. I can still see Reynolds kicking ball after ball after ball into the outfield as Tillman throws pitch after pitch and doesn't even make it out of the first inning. It was brutal. It didn't help that the O's were really struggling at the time, having lost 6 of their last 10 games. That game just felt like the final nail in the coffin of the 2012 season for me. Luckily I was wrong.
And then last year, while we were all still clinging to the possibility that the O's might, just might, somehow be able to stagger into the post season, along come the Twins and they say, "Nope." We lost, badly, got swept and kicked off a terrible couple of weeks where the O's went 2-13. Which is still better than their record against the Twins in 2015: 0-7.
So yeah, I don't hate the Twins. I just hate losing to them because we should never lose to the Twins.