MERVYN : "I've got a Mervyn" - my knickers are wedged somewhere between my buttocks and are, therefore, causing me discomfort. In order to yank them out discreetly, one must confide in a friend, "I've got a Mervyn", so that they can walk behind you, forming a shield.
MELVYN : "I've got a Melvyn" - for some reason I have been running about in a pair of ill-fitting tights. The motion of my legs and arse has caused the tights to slowly wend their way down my thighs. The crotch is now suspended between my knees, allowing me to part my feet by no more than six inches, and meaning that the cold air is now circulating around my knickers, buttocks and upper thighs. Don't run in ill-fitting pairs of tights, you will only end up with a Melvyn.
MAUSTYN : "I've got a Maustyn" (pronounced "Moss-tin"). My sleeping bag zip is very stiff, and while I was fiercely yanking it up, I somehow managed to wedge the end up my arse. This is most painful, but results in much mirth at sleepovers. Whoever looks most uncomfortable has definitely got a Maustyn.