Baby hissing when touched

My neighbors got a bearded dragon a few weeks after I did. They found out that I owned one too, and invited me over to see their set up. They didn't have a heat lamp. They just had a UVB and a desk lamp that gave off no heat, and a heat pad stuck to the side of the tank. They got their baby from Petsmart. When I saw it, it looked sick and weak, and no more that three weeks old. I told them what I thought, and that they need more heating and things that they already had. They have only been feeding it live crickets and a bit of celery once a week(celery gave Bodhi diarrhea, so I don't think this was a good veggie choice).
I went over there again just two days ago to see how it was doing. It's in their basement in the boys' bedroom(it was a Christmas present like mine), but the boys' have stopped caring for it and the responsibility has fallen to my friend who asks me questions as if I am a vet. When I saw it, it looked no bigger than it had two months before. i reached in to handle their baby, but as soon as I touched it, it hissed like a wounded animal does. I nearly cried as I listened to it's whine and saw the sadness in its eyes.
The beardie has a heat lamp and a large UVB, but only after my instruction. They heat pad is still there, but I'm not sure if it's doing anything good or bad. They have not increased the vegetable intake. I have recommended that they take the poor thing to a vet, but I didn't want to sound like I was telling them that they were terrible owners. I am very scared for this baby. Someone please help, I can't figure out what is wrong with this unfortunate beardie! (they have named it Edmund, but still don't know the gender.)

It doesnt sound like a great setup for the beardie. Maybe have your neighbors check out my blog. I have an extensive intro to owning a bearded dragon, and it could help them.

http://scalesntales365.blogspot.com/2017/05/guide-to-owning-bearded-dragon.html?m=1

Poor baby is a wounded animal and is acting out after being in poor conditions for an extended period. Have they improved his nutrition at all along with the lighting? It's a fine line between telling someone what to do with their "property" and offering advice to help and moving too far in either direction won't wind up doing any good. I would keep offering help and limited advice (saved for the most critical areas) for now. If they're asking questions you aren't familiar with the answer to or or unsure of feel free to post it on here and we can try to help as well. I certainly they take your advice to heart and improve his life soon. He can probably be helped but it will take effort and care on their part.

The lighting is good. They have a good heat and UVB. I am worried about what effects the heat pad is having on him. I heard that heat rocks are bad, but are pads? The pad they have is just stuck to the glass and I assume it keeps him warm at night....

Some people use the pads and like them. The main concern is them malfunctioning and causing burns like the rocks do but I don't hear of it happening much. They heat by contact so they'll heat part of the tank but won't radiate warmth. I prefer to use overhead heat to warm the air in a whole section of the tank. I use a MegaRay heat projector and it works well for overnight heat when needed. I have it on a dimming thermostat so it only kicks in when the tank drops below 70 overnight.

Would a way to help which should only be perceived as 'friendly' be to give them some of your spare greens? If you're handing them some collards or dandelion under the guise of 'my beardy loves this, have you tried with yours?' Its not like you're critisising them, yet may improve the celery situation.

Ugh. I feel for you and their dragon though. Such a sad example of people buying an animal with no research.