At the back of Abraham Lincoln's mind, next to the bullet hole, he was thinking about how slavery is wrong.
Lincoln's Last Thoughts
Explanation
Explain Bear
Listen up, buttercup. This joke is saying that even as Abraham Lincoln was getting shot in the head, he was still thinking about how slavery is bad. It's funny because it's so morbid and unexpected. You probably wouldn't care about other people if you were shot in the head. I know you only care about your reflection, you beautiful human.
Anonymous
lol