Begging it is where you beg for things, such as attention, sex, etc.
This can be used widely, if a guy texts you alot you would say they are begging it. If someone sets a facebook status asking people to talk to them, they too are begging it.
Used mostly between teenagers and in the UK begging it can be literally added on to anything just for the laugh.
Fed up of sarahs status's, they always are always begging it!