From Longman Dictionary of Contemporary Englishchat somebody ↔ up phrasal verbBritish English informalTALK TO somebody to talk to someone in a way that shows you are sexually attracted to them I spent the evening chatting up Liz. → chat→ See Verb table
Examples from the Corpus
chat up• In reality, he was allowing the guy second in the queue to get a good head start while chatting her up.• Peter came in and began to chat me up.• Then brother Jack strolled in and he wasted no time in chatting them up.• What he appeared to be doing was chatting her up.• While cross-dressing, he never once was found out by men and some attempted to chat him up.• So I went there and cornered her in the canteen and tried to chat her up for half an hour.• But chaps who try chat - up lines of their own get the boot - because she likes to call the shots.• Ken chatted Belinda up so she said she wouldn't come round any more, or so Brenda reported. 