The hilt and pommel remind me of the Swiss type of dagger but the 'Malchus' shaped extremely curved blade clearly seems to reflect Oriental influence.
On the one hand, we cannot generally rule out that such a type of dagger actually existed. On the other, as David and Fernando have put out, this is Hieronymus Bosch. He is well known for his satirical, drastically overdrawn and 'fantasy' style of paintings, their characters and old style equipment. Often his paintings contain allusions to old sayings, and the faces, bodies and accouterments of his persons are both surrealistically and cinically distorted. His range of grotesque fantasy was unique among the late medieval/early Renaissance painters.
Of course, the formal style of the first dagger shows characteristic late Gothic elements, so it may not be pure fiction. The ballock dagger obviously is completely authentic.
Anyway, this is a really great thread as it shares my love of period artwork sources - they are most important when it comes to discussing original objects!
Best,
Michael