In British culture - the handshake is the default greeting. It's as ubiquitous as a hearty "good morning" or offering to buy people a round of drinks in the pub. To deliberately not shake hands is rude. It indicates that you are breaking normal social behaviour.
Handshakes are political. Back in the 1990s, the Prime Minister shook hands with the Sinn Fein president - leading to protests:
"Traitor," they shouted. "Your hands are covered in blood," they barracked him. The loyalist protesters were waiting, some wearing rubber gloves to show what they thought of the Blair-Adams handshake.
A woman yelled: "You are contaminated, I'll not shake hands with you."
Blair barracked after historic handshake with Adams 1997
I think I've only ever refused to shake hands with someone on a couple of occasions. Once, a director of Phorm - a company which tried to blackmail me - came to my office. I don't think he knew who I was, but looked aghast when his proffered hand was refused.
Another time, a noted homophobe in the UK tech scene bounded up to me like we were old friends (we barely knew each other) and stuck out his hand. I looked at it, turned around, and carried on talking to my friend and his boyfriend.
I don't regret either - but both cases left me feeling uncomfortable. Like I'd spat on their face, or insulted their parentage.
A few weeks ago, I was at a health-tech conference.
— Terence Eden (@edent) March 4, 2020
Handshaking was discouraged, but not banned. I took the stance that I wasn't going to touch anyone. And yet - even in a health conference, with COVID19 bearing down on us - people were still offering their hand to me. I tried to laugh it off, or offer a foot bump, or elbow knock.
Some people glared at me - as though I was personally accusing them of being plague carriers.
It's a fundamental shift in social norms. And it feels weird. I wonder if it will continue?