The study had the aim to find out what attitudes high school students and their teachers had towards slang expressions from the English language, in which situations the students used slang, where they learned these expressions from and if there were any differences between boys and girls. The methods used were both (a quantitative method by using) questionnaires for students and (a qualitative method by) interviews with teachers. The result shows that students were positive towards using English speaking slang and they mostly used the expressions while communicating with friends or online. The students learned slang expressions from social media platforms and other websites, music, film/television series and friends. The teachers had a neutral attitude towards slang and their view on the matter was that students had difficulties in using formal English since students learned informal English from popular culture.