If you get your thumb closed between two car doors, by all means go back to the house and don't play tag with the rest of the birthday guests. Take the ice and painkillers offered by the GOH's mother. Call your parents to let them know what happened, and take their advice over the phone. Ignore what the people who are in front of you and can see the damage are saying.
The next day, when your parents finally see your thumb, which has a rather large dent just below the cuticle and is swollen somewhat epically, continue to listen to them when they say it's not worth going to see a doctor. Even when the nail falls off.
To this day, I don't know if I actually broke the thumb or not, I never saw anyone. Dad convinced me that they'd only be able to tape it and give me painkillers, it would have only been the tip of my thumb. I think I did, though, because I can feel the weather change, and that knuckle has been able to pop funny since then. Oh well.
Oh, and another one!
When using a very sharp paring knife to try to pry open plastic covers over Christmas style lights and it slips and goes into your finger, please run to the bathroom to get it washed out and covered. When you bleed through a quartered gauze pad and bandaid in five minutes, go replace them. Don't bother calling your parents, tell your sister you're fine, and deal with it. Because it's just a small cut, half an inch wide, it can't be that bad, right?
Right, it took three weeks to heal, and by the time my parents finally caught me changing the bandaid after the first week and they could see how bad it still was, they told me I probably should have gotten stitches.
So don't be me when it comes to "minor" injuries and getting them seen by professionals.