Old-school UK slang with a couple of flavours. Most commonly, a growler is a right moody so-and-so who’s always moaning and snapping at everyone, especially first thing. In a few parts of England it can also mean a pork pie. Either way, it’s not exactly sunshine and rainbows, is it.
"He’s a proper growler in the mornings, stomping round the kitchen like the bins owe him money. What cheers him up? Nowt, till he’s had his third coffee and a bacon butty."