Everyone stops eating meat, dairy at once causing a huge collapse of industry and supply chain jobs. Farms haven't had time to switch use to plants only causing starvation.
No new giant projects are launched because, everyone wants to sit and relax and deal with current issues while sipping a drink on the porch.
Public transit is overloaded as everyone realizes everyone owning a car is a ridiculous and wasteful idea.
There's a good amount of wasted food that could be used, but you suddenly have a whole world not eating meat, eggs, dairy, and all plant based, then there will be a temporary shortage on everything