It means to make-out voraciously. Term is used more when people see you doing it publicly. Not necessarily a bad thing but people say it more disparagingly.
to kiss for a long period of time, may include (hopefully) some biting and licking of the neck and ears. non-pretty way of saying make out.
Nineteen-year-old Louisa Almedovar and her 22-year-old boyfriend Rich Langley, both of Vineland, New Jersey, USA, sucked face non-stop for a record 30 hours, 59 minutes and 27 seconds on December 5, 2001
guy 1: ew. they're sucking face.
guy 2: yeah, they must really like eachother.
guy 1: no way. its just really fun.
guy 3: yeah. sucking face rocks fucking shit man!!
By Blake
Suck Face
To kiss so hard/intensely that one or both partner(s) are literally sucking each others faces