Colloquialisms are expressions that we use in casual or informal conversation. They are quite quirky, and vary according to your age, background, ethnic origin etc.

In formal and academic writing, colloquialisms such as:

and other similar expressions should be avoided. Also, avoid rhetorical questions:
Rhetorical questions are a waste of words.

In addition, colloquialisms are often generalisations, for example:
But how much is 'a lot of'? How big is 'really big'? How small is 'quite small'?

In short, there are two reasons to avoid colloquialisms:
  1. You won't find them in academic books or journals and since, whilst at the university, you're part of a community of academics, you should tailor your language to suit the academic environment.

  2. Colloquialisms are easily misunderstood by readers who don't share the writer's background, and are usually imprecise.