We can't see this girl's face, so we don't know whether she's wearing this message ironically or sarcastically, or she really is inviting people to come and try to unlock her using the method suggested! Anyone who knows a smartphone knows where it comes from - technology has brought all kinds of different new phrases into our day to day language, and this is one of them. Apparently, if you want to unlock the girl's top, all you have to do is rub her up the right way!
Innuendos are commonplace on t-shirts for young people - especially when they're planning a big night out, and they want to show the world how confident they are - so we'll award this one extra points for being quite clever about it, instead of resorting to outright filth! Perhaps she should also consider asking prospective suitors to enter a passcode?