ševiti

1. vulg. slang (ševiti se s kim) to have sex; to screw around
   Ševili su se do jutra. — They were screwing until morning.
2. vulg. slang (+ acc.) to fuck; to screw
   Čuo sam da on ševi svoju šeficu. — I heard he's screwing his boss.

A crude colloquial word used in both Serbia and Croatia; close synonyms are jebati, tucati (se), kresati (se).