1. Both Kurt and Blaine are teachers at a school/university and are married but didn't want anyone to know so started bickering and fighting but decide to let all the other teachers know on their 25th anniversary.
2. Blaine is a professor and has the people in his class come with him to volunteer at his nieces school. Kurt keeps going with him to spend time with him. They become close but nothing happens until after Kurt finishes Blaine's class.
3.Any AU especially with Teacher(both adults), Fashion Designer, Policeman/Fireman.