Considered a violation of their laws... (link)
Those weird and wonderful Guatemalan laws that if you're not careful will see you dragged up some temple steps only to have your heart cut out with an obsidian blade.
Hang on a sec; we're not exactly talking necking a bottle of Havana Club in public on the streets of Riyadh, stepping on the King's portrait in Bangkok, chewing gum in Singapore or bringing your dog with you into Australia, are we?
If it had been Pepito travelling in the other direction, I think attempting to board a plane with a backpack full of bullets might well have been considered a violation of US Federal law, and that the TSA might also have been disinclined to regard this as an innocent mistake in the first instance...don't you think?
I was once severely hassled over some instant coffee which they insisted had nitroglycerine amongst its ingredients, only to later admit that it's an ingredient in many common consumer products, such as hand cream.
But they do so like making you squirm anyway. My (very) Norwegian friend by the name of Solheim was even held up because his surname sounded suspiciously like Suleiman.