Can I make attacks non-lethal?

Question

Sometimes my party is being incredibly stupid, and it makes me want to punch them in game for being stupid. An example of this is trying to use a party member as a live test subject for a mushroom that we have a book that tells us what it does before checking the book. The only problem is that the person holding said book is the wizard, and my unarmed strike is 4 damage, and we're level 1.

Is there a way to make this attack non-lethal so I don't accidentally kill my party member with a crit? I already checked the basic rules, which is the only book I own that isn't monsters, races, and/or a campaign, as I didn't buy the phb or DM guide yet, and I didn't find anything.

Sorry if this was already asked, I couldn't find it if it was.

Edit: I'm looking for ways to reprimand a teammate for being stupid, and just making it non-lethal without anything else would knock them out still, and they might forget why I reprimanded them in the first place. Sorry for not clarifying sooner. For example, is there a way to make sure they don't fall unconscious while still hitting them? I can't grapple because I'm 2 sizes smaller, I just want to make sure they know not to do it again.

This is the literal exact same question that was referenced before when it was closed last time. I explained why this is different already.

Answer 1

The rules for knocking a creature out are found in the Damage and Healing section of the combat chapter:

Knocking a Creature Out

Sometimes an attacker wants to incapacitate a foe, rather than deal a killing blow. When an attacker reduces a creature to 0 hit points with a melee attack, the attacker can knock the creature out. The attacker can make this choice the instant the damage is dealt. The creature falls unconscious and is stable.

That said…

PVP combat should be avoided unless everyone is on the same page about it.

Be very careful with PVP. Player-versus-player combat can very easily lead to sore feelings if it is not agreed upon beforehand. In your case, I recommend talking about this out-of-character with the other players at the table before hand. If the other players are not into PVP scenarios, you might cause unnecessary out-of-character conflict by punching them in-character.

Answer 2

Ask your DM for "The Slap"

As Thomas Markov's answer stated, you can use the rules for knocking a creature out. However, you'll still deal full unarmed damage, which can be annoying, especially on a crit.

You could also decide to keep those attacks as "flavor" interactions, making them deal no damage at all. While this works, some players may prefer to see the effects of this kind of interactions reflected in the numbers and as dice rolls.

As my groups are very much of this kind, the solution we devised is what we called The Slap. We agreed with our DM that when we wanted one of our characters to punch another in the face, be it for comedic effect or any other kind of flavour, the character would make an unarmed strike that would only deal 1 damage, ignoring crits and all other damage modifiers.

While we called it a "slap", this attack took many different forms depending on the character and the situation, and so we gladly repurposed it as punches, kicks and even tail swipes.

This simple homemade solution allowed us to have our fun during roleplaying situations and have it take effect through our stats, while keeping it minimal enough that it didn't frustrate players when HP mattered.