Warning: Contains SPOILERS for The Menu.
This article contains discussion of suicide.
Chef Julian Slowik (Ralph Fiennes) says something to Tyler (Nicholas Hoult) that becomes a pivotal turning point in The Menu, but exactly what he whispers is left a mystery. Although Chef Slowik is the one who has brought the diners together in order to kill them, Tyler is arguably The Menu's biggest villain. The one guest who knew what was going to happen, Tyler is the most deceitful and selfish of those invited to experience (and die at) Hawthorn, allowing everyone to perish and even bringing a date, just so he can indulge in gourmet luxury to validate himself.
Ultimately, then, what happens to Tyler in The Menu is his own doing, but Chef Slowik does play a part. After revealing Tyler's part in the plan, the chef invites him up to cook a dish only to humiliate him. But what's most interesting isn't what's clear on screen, but what The Menu decides to hide. After his terrible effort at making a meal - "undercooked lamb, inedible shallot-leek butter sauce" - the chef whispers something to Tyler, which changes his fate completely.
What Chef Slowik Said To Tyler Made Him Kill Himself
Although what Chef Slowik says to Tyler isn't revealed, it clearly has a profound impact upon him, because it leads directly to his death. Tyler is later shown to have hanged himself, and it's what Slowik whispers to him that makes him do this. Chef's words could well have included pointedly telling Tyler to kill himself, but it's also likely they carried more of the utter disdain he had for the gourmand. Humiliating Tyler wasn't part of Chef Slowik's plan, which means he was originally intended to die with the others - something he was clearly prepared for (he didn't even try to escape when they were outside).
Tyler was a fawning foodie, and worshiped at the altar of Chef Slowik, and so believed taking part in this dinner - despite knowing he'd die - was set to be a transcendent experience for him. The humiliation of his attempt at cooking was then likely followed up the Slowik's own harsh words, not only telling him to kill himself but also outright rejecting him. Slowik presumably whispered that Tyler would not only never earn his praise, but also was no longer considered worthy of being "part" of his menu. That was, perhaps, a fate even worse than death for Tyler, leading to his suicide before The Menu's ending.
Why It's Better The Menu Doesn't Reveal What Chef Whispered To Tyler
It's an interesting choice for The Menu not to reveal what the chef whispers to Tyler, when it otherwise doesn't hold back - character motives and why people are killed are well explained. It's also a smart decision though, because not knowing Slowik's words make the moment even more impactful. Firstly, it allows Tyler's death to be a bigger reveal to both Margot (Anya Taylor-Joy) and viewers, since it's not initially explicit what happens to him after his cooking disaster.
Not confirming what Slowik says also makes it a more intimate moment between them. This isn't just a failure, but an incredibly personal condemnation and rejection of everything Tyler does and believes in. It would almost be easier for him if it were done publicly - like sous-chef Jeremy (Adam Aalderks), it would make him more involved in the experience. But doing it privately excludes him, the ultimate shame for the person so obsessed with preaching his love of food he takes pictures of it when he knows he's going to die. The Menu's chef wants to kill everyone, but Tyler is the one he most actively despises, and whatever he says confirms it.