octopaniac
a person who can't focus on anything else because they're too busy thinking about octopuses and their weird habits.
My octopaniac friend forgot his homework because he was too busy watching videos about octopuses changing colors.
I asked my octopaniac brother for help with math, and he started talking about octopus ink instead.
My octopaniac cousin wouldn’t stop talking about octopuses at dinner. I had to eat my broccoli in silence.