počastiti

1. (someone + instr.) to treat
   Počastio sam ih pićem posle utakmice. — I treated them to a drink after the match.
   Komšinica nas je počastila kolačima. — Our neighbour treated us to some cakes.
2. (počastiti se + instr.) to treat oneself
   Posle ispita sam se počastila tortom. — After the exam I treated myself to some cake.
3. ironic (someone + instr.) to shower; to treat
   Vozač ga je počastio psovkama. — The driver showered him with curses.

The treat goes in the instrumental: počastiti koga pićem; the imperfective is častiti.