ur mum

This phrase is used (mostly in England) as one of the best way to end a conversation. The reason for this is because there is no way to reply to it.

Example 1:
Joe: What do you want for dinner tonight?

Jeff: Ur mum

Example 2:
Bob: Harry you’re so ugly

Harry: Ur mum

Example 3:
Teacher: Harvey, did you do your homework?

Harvey: No

Teacher: Why not?

Harvey: Ur mum