He may have some retained sperm plugs. That would be my guess that he's big in that area.
You can try soaking his bulge in some warm water to help him pass it. Also try warm showers aswell. Just put him on a plant and aim the shower head at the wall so it bounces onto the plant. You can do this for 15-30 minutes.
You can help your big boy out by gently rubbing his bulge to loosen up anything while he's soaking in warm water. Another thing members do is rub KY Jelly on their vent to help moisten up sperm plugs to prevent any damage from them being pulled. If you see any sort of booger like thing hanging out you can use some tweezers to pull it out.
If not, and he acts completely normal then don't worry about it. Your boy is just gifted
Oh, and yes...I did say rub KY Jelly on your chameleons genitals. haha
The second picture you attached does make him seem like he's a bit on the BIGGER side. My chams just had a smooth bulge after their vent. Your's seems like it's way bigger than normal.
Is he acting any differently than usual? Do you ever see any sperm plugs laying around his enclosure? They look like boogers on branches sometimes and you can catch your cham dropping them by rubbing his vent on branches.
Another question is do you ever see him prolapsing? Meaning seeing red tube like things come out of his vet area? (hemipenes aka private parts)
Hopefully you can help him out with the KY and warm water. You can also try using warm water and sugar if you don't want to use KY. KY Jelly (lube) is just what i've heard other members use.
- Btw I think you get the funniest thread title award in the history of CF.