You can say you’re friendly on a resume by framing your friendliness as a soft skill. For instance, you can list interpersonal skills or people skills in your resume’s skills section.
Soft skills like friendliness are valuable in every industry, and show employers that you can work well with others if given the job.
To prove how friendly you are on your resume, highlight instances of working well with coworkers or customers in your experience section. For example, you could say you had a 99%+ customer satisfaction rate in your last job as a customer service representative.