OK, here's a good joke that works in Slovene and in Croatian, but I'm not sure if I can translate it in English (so it would stay funny).
A guy drives up to the border and the border inspetion stops him.
"Do you have anything to declare?"
'I only have a calculator with me.'"Let's see."
And guess what - he had a machine gun in the back.
"What kind of a calculator is this?!?!"'I calculated there'd be trouble...' 
A evo i hrvatskog originala, za one koji razumete:
Vozi Siptar prema Srbsko-Albanskoj granici i zaustave ga:
"Imate nešto za prijaviti?"
'Samo kaljkuljator.'
"Pokažite."
I vidi ti njega, on izvuče kalašnikov.
"Ma kakav ti je to kalkulator?"
'Idem da sredim neke račune...'