Put it right after the reveal that someone has turned up uninvited, then follow it with the Bruh Meme sound as the next reaction, and save the It Was At This Moment He Knew clip for the cutaway that explains how they got there.
About this sound
This is a short spoken Czech line, about four seconds long, in which a voice bluntly asks Shermane what they are doing here. It lands as a sharp, funny confrontation, the kind of direct challenge that makes an unexpected arrival feel awkward and exposed. The line comes from American Pie.