Does drafting cause resistance to the lead rider? I know that when riding close to another cyclist, I expend less energy to go the same speed. But does the Conservation of Energy "law" mean that the lead cyclist is going to expend more energy to allow me to expend less?

(i.e. Is there a physical reason to get angry at someone drafting behind you? Does riding in their slipstream cause drag for them?)
No, on the contrary the lead rider also gets a boost.

The reason to be unhappy about someone drafting you is that they're too close to be able to react if there's a problem - if you go down they will run over you.

The way I understand the boost is that a solo rider is effectively dragging around a volume of low pressure air - you push the air out of the way creating a high pressure volume in front of you, but that displaced air doesn't magically close in behind you, it flows out then flows back, creating a "missing air" volume behind you. If something fills in that space you don't get sucked back into it as much. There's a mention on wikipedia chain gang (riding) which links to the exploratorium article but not to a primary source that I can see. That explanation is common and makes sense, so I've never chased it further.

Here is a link to a wind tunnel video which shows that the lead rider receives a small benefit from having a drafter.