I am not sure what you mean by 'body language' in the given context. Also, the focus or importance on 'body language' [as it's understood generally] is not uniform across all functions or sectors. For example, a marketing person may need to have a lot more 'proper body language' than someone in, let's say, the Accounts function.
Also, your usage of the words 'civil company' for describing your organization is a bit confusing. Is it into Construction, civil design, Infrastructure, etc.? I hope you get what I mean, since there are a whole host of areas where Civil engineering is the mainstay.
Regarding ensuring some sort of dress code is followed, while a formal policy will definitely have to come to ensure uniformity in understanding and implementation, I am not so sure if starting the whole implementation with the policy will work. Given the type of responses or reactions you seem to be facing, the policy could be counter-productive until you handle the 'ego' part of the staff: how would be the key.
Ways to Handle the Issue
1. I am not sure of the sort of support you get from your CEO, apart from 'telling' you to educate the staff. If any policy has to be the starting point, it has to come from the CEO, and as HR, you need to implement it. That way, everyone will be clear about who is interested in this policy and also that you are just implementing it. The meeting that Pon and Archna suggested will then work very well to formulate the policy, since the chain-of-instruction is clear to all. The way I get it is this [hoping I am wrong]: your CEO is trying to fire from your shoulder, since, for whatever reasons, he doesn’t want to use his or her own.
2. If the support you can expect from your CEO is, to say the least, very minimal, then I suggest you don’t talk of any policies at all to begin with. And also, never ever give the impression that you are educating them. First of all, you are new here, and added to it, you realized only later about their 'ego' issues. I see a clear message in their 'anger': Who are you to teach or tell us now when we are living like this in this company without any remark from the CEO all these days or years?
The only way I can see you succeed [without your CEO's support or direct involvement] is to first endear yourself to them and only then raise the issues where you are not getting cooperation now, but would like to.
How to Proceed?
Frankly, I would leave this open to debate, since the right workable advice for this query could need many other inputs from your end depending on the thoughts or suggestions the members of this forum may come up with.
Regards,
TS