First, we have to clarify what we mean by "sherbet", as the word means different things on different continents. If your Australian friend invites you for a few sherbets, most likely he is suggesting to have a few beers at the pub (or bar, for Americans).

For Americans, a sherbet is a (usually quite sweet) water ice (excluding any dairy product, which bring along the advantage of it being a vegan desert). 

Here, I will use the word sherbet loosely. The trick of a sherbet is in the balance of sweet and tangy, and having a good kitchen machine available to blitz the mixture to perfect smoothness. 

Some combinations work really well. Strawberry, fresh mint and dry white wine, for instance. Sweeten to taste and realize that once chilled, you will not taste the sweetness as much as at room temperature. Blitz with ice cubes to create an instantly cold surprise, or cool down in an ice machine, should you have one. If you chill the mixture in the freezer, take it out every 20 minutes or so to break up the ice crystals.

Another great one is raspberries and desert wine, or strawberries with oat milk. Be creative, use what you have and decide how you want to serve your sherbet: frozen, half-frozen (semifreddo), granita, liquid with a straw, ... One note on raspberries: even when blitzed for quite a while, the little seeds may still be intact. Consider first blitzing the raspberries, then using a sieve to filter out the seeds, before putting back into the machine. 

In order to create a little contrast in textures, consider sprinkling some (caramelized) pistachio nuts on top.