Research on potential interactions between Lipitor (an HMG-CoA reductase inhibitor used to lower cholesterol) and Vitamin C is limited, but available data does not indicate any major issues (DrugPatentWatch.com) [1].
The US National Institutes of Health (NIH) states that taking Lipitor and Vitamin C together can potentially cause gastrointestinal side effects, including diarrhea, stomach pain, or upset stomach (NIH) [2]. A case study found that a patient experiencing a severe and prolonged gastrointestinal bleed had taken a combination of Lipitor and large amounts of Vitamin C (National Library of Medicine) [3].
The effects can be mitigated by maintaining a balanced diet, not consuming excessive amounts of Vitamin C (over 2,000 milligrams per day), and discussing any concerns with your healthcare provider.
Sources:
[1] https://www.drugpatentwatch.com/
[2] https://www.ncbi.nlm.nih.gov/books/NBK554417/
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4301811/