I think it depends on the formality required in different cultures. Here in the US, you can definitely use those expressions in all those situations. They're informal, but then again, many interactions in the US are informal. Unless you're a service provider, then you should definitely be more formal when speaking to your guests and customers. In the UK however, you might want to use more formal speech in situations such as with a doctor, or an airport employee even if you are the customer.

Hello, Bogdan. That's a good question. In the United States, these expressions are definitely informal, but they are not necessarily rude. I would be careful about using 'pain in the ass' with a supervisor or a doctor (although it depends on how informal they are). 'It sucks' could definitely be used with an airport employee, shopkeeper and doctor. I doubt you would offend anyone (in the U.S.) using 'pain in the ass', but remember it is an informal expression. You should use it when you are already on friendly terms with someone. It's probably not a good idea to use it with someone you just met.

Hello, Bogdan, I bet you will get many different answers depending on the age of the respondents and maybe where they live. I'd say these are very rude expressions, but also they are very common. In the US we hear them on TV, in the movies, etc, even relatively small children sometimes use them, and teenagers, definitely. I would not use with anyone I do not know very well, or someone to whom I want to show respect. They are not terms I would use with older family members, other professionals, or anyone in a business or professional setting, even though the expressions might be tolerated.Just my two cents' worth!