It is an expression that literally means "to kiss the door". "Otišao sam i poljubio vrata." - "I went [there] and kissed the door." An entry can be found in [this Croatian dictionary](http://hjp.novi-liber.hr/index.php?show=search_by_id&id=eVtuUBk%3D). Alternatively, it can mean not being allowed to enter by force. "Možeš da dođeš, ali ćeš da poljubiš vrata." - "You can come over, but you'll kiss the door."