With toe-stubbing swearing, the actual expletive used is functionally immaterial. It’s the act of letting off steam, emitting some pent-up emotion that speaks, if you like, independently of the words used. This semantic vacuum is highlighted by the secondary meaning of the word ‘expletive’, that is, ‘any syllable, word or phrase conveying no independent meaning, especially one inserted in a line of verse for the sake of the meter’, such as ‘Tra la’ in ‘The flowers that bloom in the spring, Tra la’. That’s one to remember next time you get pulled up for swearing.
(Language Most Foul, Ruth Wajnryb)
The quote in the above passage comes from a song from The Mikado (as if you didn’t already know). An example more appropriate to the season might be:
Deck the halls with boughs of hollyThere are similar examples of expletives (in the secondary meaning) in Latin poetry. The ubiquitous use of ‘O’ (e.g. when addressing a god) could be understood as an expletive – a meaningless word, expressing emotion, inserted into verse for the sake of the meter.
fa la la la la, la la la la
Another sort-of-example comes from a (relatively) well-known line of Ennius:
at tuba terribili sonitu taratantara dixit
The war-trumpet with terrifying sound blew taratantara
taratantara here is the onomatopoeic sound of the trumpets, but you could see as a bit of a line filler (and thus an expletive) as well.