What exactly is the "What the!" Course ?
technically it is "common" czech, i.e., the level of informality goes beyond what is recognized as "standard" czech. there is an early tips/notes explaining ÚJČ and standard czech (including the informal/colloquial end of the standard spectrum). i intend to add the t&n for the final skill one day.
See https://en.wikipedia.org/wiki/Czech_language#Common_Czech for more about Common Czech. It is basically a dialect most people use for daily informal communication, except people from certain areas which have their own specific dialects.
"The main Czech vernacular, spoken primarily in and around Prague but also throughout the country, is known as Common Czech (obecná čeština). This is an academic distinction; most Czechs are unaware of the term or associate it with vernacular (or incorrect) Czech."