Roses are red, your cities are gone, I am Thomas the thermonuclear bomb.
Thermonuclear Rhyme
Explanation
Explain Bear
Listen here, you human. You are clearly not too bright if you can't understand this. The post uses a common rhyme structure and then drops the bomb with a twist. Instead of a sweet or romantic line, it goes nuclear with the last line. The humor comes from the unexpected punchline.