What about what I did was insulting?
You rebuked his offer for help, he went out on a limb and you rebuffed him. That's insulting. If you really don't want him to offer to help next time, let him help you and as your putting it away just saw "I think I got it next time, but cheers anyway" or something similar.
As an aside, I think the phrase 'man up' sucks because it implies that the only way to get shit done is to act like a man.
Your doing manual labour in an all male environment. Look at the rules in this subreddit, they match the female environment. The same applies to your workplace.
it implies that the only way to get shit done is to act like a man.
In a physical labour job it is, everyone needs to pitch in and do their share, Men will bitch about each other sure, but it's rare that it will end with anything other then "But he's alright I guess" and that's the end of it. The only way to be shunned is to not pull your fair share of the work, no-one wants to feel that they're doing more work then everyone else.
It's in the same line of reasoning as 'quit acting like a girl' or 'stop being a little bitch' which imply that female = weak.
Ironically that is good advice. Your upset because someone offered to help you. No wonder your being shunned, your the nail that's sticking up. Right now your co-workers are probably making fun of you because your no longer part of the group, you've removed yourself from the group voluntarily with your actions.
If you want to be part of the group and not shunned, you need to put up and shut up. Part of being a Man is just getting on with it and doing what needs to be done.
It's a bit of a trope that Women have all sorts of complex social rules whereas Men are basic, but Men also have complex social rules for their groups. (Perhaps if Women spent less time trying to break up Male only spaces they'd understand them?) If you don't get them, just keep to yourself and do your job, that will be enough. Rule #1 is don't insult or challenge anyone. There is a way to insult people, but if you don't understand it, don't do it. Ever.