Tapping up is the attempt to crack onto somebody, not necesarily involving intercourse, maybe just a cheeky pull. It can also can be used in the context of failure.
"Tim tried to tap up that girl last night but failed"
door Hertford College 15 mei 2008
An English slang word word meaning a bribe
"If you need to get your motor through it's MOT just tap up Bill and he will sort you out"
door Darrenwl 7 februari 2007