'Yass' (also 'yas', 'yaaas', 'yassss') is an enthusiastic, drawn-out 'yes' expressing excitement, agreement or hype — popularised in American drag and ballroom culture, mainstreamed via the 2013 Broad City episode where Ilana Glazer made it a national catchphrase. If your teen says 'yass queen' to a friend, they are hyping them up. Harmless and friendly.