Grina means 'to cry' or 'to grimace' (potentially with negative, 'whiny' connotations but not always) if you're in Svealand, central or northern Sweden. But head to the southern Skåne region and the same word means 'to laugh'. Very confusing if you're telling someone they make you grina. And to add to the struggle, in some parts of the country it can mean either of the two.
The mystery deepens: in Danish, grine means 'to laugh' and in Norway grina means 'to cry'. So how did one little word come to have two contradictory definitions?
It all started with an Old Germanic word which meant 'to gape open', and in fact you'll also hear grina used in this original sense, for example if someone says luckan grinar (the hole gapes).
Then people across Scandinavia started to use grina to describe wide open mouths, while in Old English the verb grennian developed in parallel, and was used to mean 'to bare one's teeth in emotion', which was usually associated with pain or anger. That's where the English verb 'to grin' comes from, and in the southern parts of Scandinavia, grina evolved along the same lines, and was used to describe people opening their mouths wide in happiness or joy – laughing.
But an open-mouthed expression can also show pain or sorrow, and that's the direction grina took further north and east in Sweden (as well as in Dutch and German, where grienen and greinen mean 'to whine'). This is also where Swedish gets the related adjective grinig, which means 'petulant' or 'grumpy' – picture a toddler protesting a perceived injustice.
Jag grinar av lycka
I'm laughing/crying with joy
Det kommer inte att hjälpa dig att stå här och grina
It won't help you to stand here and cry/laugh