Putting my booze snob hat on, G&Ts are preprandials (ie for drinking before the meal), after a meal a cultured person would drink port, brandy, whisky or possibly a liqueur.
(Personally I’ll drink any or all, before, during or after a meal, but I’m a peasant)
Your colleagues are ignorant, Sauvignon Blanc is the grape used in Pouilly Fume and the main Bordeaux whites, all very posh wines.
I bet they won’t drink Chardonnay, but would love a white burgundy…. White burgundy IS Chardonnay! Again very posh. (Hint, try the Waitrose own brand white burgundy, horrible blue label, but lovely wine and amazing value).
Red wines tend to have a more assertive flavour, so go better with red meat, whites tend to have a more subtle flavour, so go better with fish or chicken. But there are some white wines that will stand up to anything, similarly some reds will work happily with lighter food. And there are some amazing rose wines which go with anything.
None is posher than the others, as the French will tell you.
Wine is meant to be enjoyed, so drink what you like with whatever you want!
I would suggest that you widen your palette by trying other wines, a whole new world of pleasure awaits. But if Sauvignon Blanc is what you like, go for it!