The threat of a serious reprisal.
This phrase originated in Britain. It may well have had a literal meaning since it was first used in the Middle Ages, when disembowelment was used in the UK for torture and execution. In these more enlightened times the expression is limited to figurative examples like, “I don’t want to tell Mom I’ve lost the car keys – she’ll have my guts for garters.”
A printed reference to ‘guts for garters’ appears in Robert Greene’s The Scottish Historie of James the Fourth, circa 1592:
“Ile make garters of thy guttes, Thou villaine.”
History does not tell us whether that was a literal threat and whether people did actually make garters of the guts of their enemies. I can find no direct evidence of a documented example of such a practice, but it is certainly quite plausible. Worse things happened; the punishment of ‘hanged, drawn and quartered’ was on the statue book in England until as late as 1790.
There are several other instances in the 16th and 17th centuries of allusions to the use of someone’s guts being made into garters – “Sir, I will garter my hose with your guttes” and so on. The earliest use of the actual wording ‘guts for garters’ that I can find comes from a long time later, in from a piece by William Curry, in The Dublin University Magazine, 1843:
“I’ll butter my knife in him, and give him his guts for garters.”
Another old example is from The Bride of Lammermoor, by Sir Walter Scott, published in 1819: “He that would not pledge me, I would make his guts garter his stockings.” In later times, it’s been Cockney low slang and was a common reprimand or threat by NCOs in the services during World War Two and afterwards.
The persistence of the expression may owe a lot to the alliteration of guts and garters, but also to the existence of similar phrases such as to hate somebody’s guts.
And it sounds like a serious, blood-thirsty threat, doesn’t it? I remember my mother, who was British, telling me she’d have my guts for garters if I did something I’d been told not to do. Being rather literal-minded, even as a kid, the vision of someone yanking my guts out was so real that I took the threat to be actually possible.