'Ey..! What you lookin' at..?!

Quietly say "Nothing" and turn away.

Turn away without saying anything.

Hold his gaze but remain silent.

"I don't know, but it sure is ugly..." (Antagonise him)

"What are YOU looking at?" (Challenge him)

Forget this nonsense and go upstairs to your room.

Hit him with an icy glare (Intimidate him)