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"
ayon kay Hertford College ika-15 ng Mayo, 2008
1 more definition
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"
ayon kay Darrenwl ika-07 ng Pebrero, 2007