A universal and impersonal way of dismissing the point of view of others.
The use of the phrase is not regarded as disrespectful, rather, when used in general conversation it implies that the topic/concept of discussion requires no further thought or consideration. This may be because the topic/concept raised is already widely know and therefore further consideration is redundant, or because the topic/concept is so absurd that expending the energy to consider the issue further would be considered an inefficient use of time.
People who use the term ‘yeah cool’ are generally cooler than those people who do not use it.
Example 1 (redundant)
Person 1: I went down to the shops and bought a loaf of bread but forgot to ask the baker to slice it.
Person 2: yeah cool.
Example 2 (absurd)
Person 1: Im not going to invite meerkats to my wedding because they are unlikely to be seated at the appropriate time and would be too busy watching for intruders to appreciate the ceremony.