You're not alone if you've ever watched in wonder as people on home improvement programs apply primer in their "good" clothes without worrying about unfortunate splashes. The fact is, primer is an equal-opportunity spoiler, but you face an excellent chance at removing it if it's still wet or less than 24 hours have elapsed since the accident. Most primers are latex-based, meaning that they're made with water, and this will increase your chance of success.
Turn the water in your sink to warm, then hold the clothing with the wet primer underneath the stream. Rub the area gently with your fingers to remove all traces of the primer.
Wash the area with warm, sudsy water.
Scrape off the dry primer with your fingers or a spoon. No flakes of the primer should remain -- only the stain itself.
Soak the spot with rubbing alcohol or hair spray, either by spraying it on or applying it to a cotton ball first.
Rub the area gently with an old toothbrush. Let the solution sit for 20 minutes.
Run the spot under warm water, then wash the area with warm, sudsy water.
Repeat the steps, if necessary, but toss the clothing in the washing machine only after you have completely removed the primer. If you don't, remnants of the primer may remain after laundering.