Is 个 acceptable for all nouns? My Chinese teacher says she doesn't care. But for future reference, is 个 acceptable as a measure word for all nouns?
No, of course. Here's a summary about the kinds of cases where 个 is inappropriate.


sth slender. e.g. 一根绳子, 一条蛇, 一条路; 一线光明, 一绺头发, 一丝细雨.

sth thin. e.g. 一张纸, 一面红旗, 一幅画.

sth solid in certain kinds of shapes. e.g. 一块砖, 一团面, 一坨泥.

sth amorphous. e.g. 一杯水, 一壶油, 一斤米, 一碗沙子.

sth forming part of a greater whole. e.g. 一层楼, 一重山, 一级台阶, 一节甘蔗, 一段木头, 一截电线.

sth where the measure words come from verbs or nouns and can't be replaced by 个 without risk of changing their meaning. e.g. 一捆柴, 一把米, 一撮毛, 一抱草, 一包糖, 一任县长, 一束花,
一串糖葫芦, 一堵墙, 一服药, 一堆土, 一封信, 一滴水, 一朵花, 一本书, 一篇文章, 一瓣花瓣.


And note that even if 个 could be used instead, the meaning might be different. e.g. 一位老先生 (respectful) vs 一个老先生 (not necessarily rude, but not respectful).

At last, this might be an opinion issue; I agree that they're understandable in daily conversion; the listener will try to supply the appropriate measure word. But IMO the abuse of 个 as measure word is not acceptable for Chinese learner, especially who want to master natural Chinese.