How to run Ansible without specifying the inventory but the host directly?

Surprisingly, the trick is to append a ,

# Host and IP address
ansible all -i example.com,
ansible all -i 93.184.216.119,

or

# Requires 'hosts: all' in your playbook
ansible-playbook -i example.com, playbook.yml

The host parameter preceding the , can be either a hostname or an IPv4/v6 address.