Come on, be more positive.
A proton, an electron, & a neutron walk into a bar...
The proton orders a shot, drinks it, then takes out his wallet and pays the bartender. The electron orders a shot, drinks it, then takes out his wallet and pays the bartender.
The neutron orders a shot, drinks it, then takes out his wallet... but the bartender stops him and says, “Wait...for you, no charge!”