Male Leopard Gecko.

Question
First off, I would love to give you the age of Artemis * My leo*, but I acquired him through the wellness center two years back when I was still working with Petco and they had had him for a while already with no recollection of how long, unfortunately. I believe he was an adult, though. I fed him a few super meal worms the other night and realized this morning that he had thrown them up. He lost his tail ( I do know that ) at one point, and it isn't looking as fat as usual. So, I proceeded to pick him up and turn him over to see if anything unusual was going on... And I saw that one testicle is much larger than the other...And that the smaller one looks to have a small puncture wound in it and a scab. I checked temperature, everything is fine and I feed him regularly. There is nothing in the cage that he could hurt himself on, and I'm worried. I'm hoping you'll have some answer as to what might have happened. Thank you for your time.

Answer
Hi Kyung,
A word of caution on super meal worms... they are regular mealworms that have been fed chemicals to stop the beetle process in them so that they grow larger.  It is recommended not to use them as food due to the chemicals.  Use regular mealworms(fresh shed are best), crickets or real superworms.
Are you referring to the area below the vent?I'm thinking you mean one hemipene was larger...is it possible that one of the insects bit him there?  That can and does happen and it can cause problems. Since you have checked the cage chances are it is an insect bite or possibly he nipped himself for some reason, such as internal parasites making him itch. You can apply some triple antibiotic ointment to the area, but do watch the area for any changes and I recommend a fecal check be done.
Vomiting  is not normal with reptiles. If it happens again, or if something else happens such as not eating,lethargic, the injury to his genital area changes, tail continues to get skinny even though you are doing all correct)then a vet visit is needed to find out what is going on.
With the tail getting skinnier....
One reason for this may be due to the insects not being properly gut loaded(fed) for 48 hours before feeding them to your leo.  This goes for all insects, including the mealworms which pet stores keep in the fridge to prevent them from turning into a beetle.
Those gel products they sell are not a balanced nutritional food for the insects. When the insects are not feed good foods, their is no nutrition in them and the leo doesn't get the nutrition he needs.  over time, the leo will suffer.
To gut load mealworms and crickets you can offer veggies, dark leafy greens, grains, fruits or special mixes designed for gut loading(not the gel things but they can be used for water)