absent-minded 

so lost in thought that one does not realize what one is doing, what is happening, etc.; preoccupied to the extent of being unaware of one's immediate surroundings.

I tried to call out to him but he didn't hear me. He wasn't paying attention. He is absent-minded

absent-minded by Snowbaby January 8, 2014

absent-minded professor 

The very intelligent are sometimes preoccupied with weighty matters (as they suppose) insomuch that they forget about more prosaic matters -- such as remembering keys, wallet, phone, appointments, etc.

The teacher showed up in class, on time -- but forgot it was Tuesday, not Wednesday -- and was halfway through the lecture before the absent-minded professor realized he was teaching the wrong subject matter. On the plus side, I understand Einstein's Theory of Relativity a lot better than I did. I hope it shows up on our Physical Science 101 exams...

absent-minded professor by 1ightsaber June 7, 2021

abcentminded

1. A gamer who isn't to fond of people better than him.
2. Will 1v1 you in rainbow six siege to prove dominance.

3. The God of all memes holy.

Person 1: He's such an abcentminded
Person 2: He always wants to 1v1

abcentminded by ABCENTMINDED68 December 19, 2019

Absentmindedstudentism 

The inability to focus; zoning out; Can also refer to professors or teachers losing their train of thought.

Ashley: What did the teacher say?.... Jim...JIM!
Jim: Don't ask me. I'm suffering from absentmindedstudentism.

Absentmindedstudentism by Mr. Alexander 34 November 5, 2010