Word or phrase for "Walking by and ignoring someone"?
In British English we use the term blanked. — ODO
- British informal Deliberately ignore (someone):
"It’s not the first time when he had duty at gate and someone had blanked him while going their way to the station."
give someone the brush — Dictionary.com
verb phrase To snub; treat icily and curtly; kiss off
"I got the brush in about two seconds in that fancy dump (1930s+)"
not give someone the time of day — Cambridge Dictionary
to not be friendly to someone and not speak to or help that person
"He kept pestering me to go out with him, but I wouldn’t give him the time of day."
give someone the cold shoulder — Cambridge Dictionary
to intentionally ignore someone or treat someone in an unfriendly way
"I thought she really liked me, but the next day she gave me the cold shoulder."
Also try snub, shun and scorn as @Dan Bron suggested
The most common word for this in American English is probably "snub":
verb (used with object), snubbed, snubbing.
- to treat with disdain or contempt, especially by ignoring.
give someone the go-by (to bypass someone; to ignore someone.) "I got the go-by from her every time I saw her."
So, go-by is one word. If you want multiple words:
cut someone dead (to ignore someone totally.) "Joan was just about to speak to James when he walked away and cut her dead."
Some other options that haven't been mentioned:
brush-off (rejection; being cast aside and ignored.)
turn a blind eye (to ignore something and pretend you do not see it.)
not give somebody the time of day (to refuse to speak to someone because you do not like them or because you think you are better than them)