Well, as a pathologist I’ve seen more than a few Pap smears* where it was evident that intercourse had occurred, if not the night before Pap collection, then in the recent past (i.e. sperm present). That does not affect Pap interpretation.
With current liquid-based Pap technology, I can’t think of anything that would negatively affect Pap evaluation other than use of lubricants, which interfere with the ThinPrep process and cause insufficient cells to adhere to the slide. We generally assume that a lubricant problem crops up in the doc’s office as a part of the exam procedure, but I suppose it could have occurred before then.
*these days very few docs prepare actual smears; the correct term is Pap test.