Be gagging for something/to do something
Definition 1 of 1
Pro Tip 1/3Colloquial Usage
Used mainly in casual, informal conversations among friends or peers. 
After the hike, I'm absolutely gagging for a pint.
Pro Tip 2/3Strong Desire
Expresses a very strong desire or urgent need for something. 
I'm gagging for some fresh air, let's go outside.
Pro Tip 3/3Emotional Intensity
Often conveys strong feelings, like a craving someone can hardly control. 
She's gagging for the latest smartphone, can't stop talking about it.