I have the following query

CREATE TABLE test_buffslip AS
SELECT
   ST_INTERSECTS(
     (SELECT ST_Buffer(geom, 0.005) FROM segments where class = 7) 
     ,geom)
FROM segments;


resulting in 

ERROR:  more than one row returned by a subquery used as an expression


I want to use the buffer created on the subquery to select features from the main table. 

Probably there are better ways to do this anyway. I am open to suggestions ;-) 


Question: Another instructor is pushing me out of the classroom right after my class ends
Answer: 
  Last time the instructor told me in front of my students that I don't understand "simple things" and that I am "playing games". 


This is where she lost her argument. You should have simply totally ignored her. Let her make a formal complaint and only respond to such formal complaints. You don't have the duty to respond to insults, or to look up what the guidelines say in response to insults. If you were violating the small print of some guidelines, then it us her job to point that out.