This, rather crudely, is what happens when you masturbate a woman who is menstruating. I first heard it in Northern Ireland, which, I imagine, is its obvious place of origin and relates to the Ulster flag.
'Don't go there!'
'You'll get the red hand of ulster!'
The Urban Dictionary Mug
One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids.
Buy the mug