Can breast cancer look like a pimple?

Sort of: Peau de orange or skin of an orange is a condition associated with breast cancer that can look like dimpling. If you have one pimple it's highly unlikely. You can have your physician examine it and decide.

Not usually: There are a number of different types of breast cancers and they can have different appearences including a generalized inflamation of the breast -- like a bad rash or sunburn. If the pimple is limited to the skin and not connected to a deeper mass it is unlikely to be anything other than just a pimple. How big is this pimple? If it does not resolve in a week or 2 have an md look at it.

Perhaps...: I suppose.... But generally the skin is not involved except in a type of breast cancer called inflammatory breast cancer.