Simon Lingeree, 26, was using shared facilities in his Mumbai apartment building – or chawl – on Saturday evening while another resident impatiently waited outside.
When he emerged from the toilet, he got into a heated argument with Santosh Kargutkar, 40, over the amount of time he had taken.
Kargutkar hit Lingeree in the head and fled the scene when he lost consciousness, police said.
The victim was rushed to hospital but was declared dead on arrival.
Senior police inspector Rarao Desai said: ‘It first started off as a war of words but Kargutkar soon assaulted Lingeree. The two of them got involved in a physical fight but there were no weapons involved.’