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1.
The male or female form of interaction, with the opposite sex, including flirting or attempting to pull.

Or more loosely defined as any interaction/banter/chilling/pulling between any guy or girl.
Jem: Mate are you schweffing tonight?
Harry: Yeah thinking of schweffing the floor 8 girls actually, fancy schweffing along?
Jem: Yeah I was gonna see if Steve was up for a schweff, but apparently he's schweffing Ellie!
Harry: OK.. Schweff ya later!
by schweffatron3000 February 23, 2011
 
2.
1. The act of sleazily coming on to a member of the opposite sex, often utilising alcohol, ridiculously colourful clothing and eye-watering lines of Austin Powers style calibre, usually delivered in an drawling accent straight-outta Surrey. A Schweffe can be of either sex.
Chap 1: Mate, did you see Georgie schweffing up Charles and the hunt ball last night? He could barely stand straight.

Chap 2: Ya, I tried to get close to ask if he was alright but she kicked me straight in the cock and told me to fuck off.
by Ballchops May 16, 2012