Calling out cousin...?

I agree w/ the doctor's comments; I would add- so long as he isn't actively antagonizing or being a drain on your family, to just let it ride until it blows up in his face... which it probably will; and to just not hangout w/ him as much as possible.

I'd keep hearing out the other answers in case others have more wisdom to add onto this.

I would say "yea, if I was still sponging off of my parents I might be able to do the same thing, then smile and walk away.

not much you can do about it, you cant control what he does

Things like this have a way of coming out sooner or later, without any help from you or others. Do not concern yourself.  Its up to the "family", as to how they wish to treat him, or respond, you will only alienate him and perhaps others as well, if you try to meddle in his messes.

I always tell my kids if it's not hurting anyone and doesn't involve you ..  mind your own business.

Living situation - that is between him and his parents, nobody else not even any siblings he has.  

There may be factors you're also unaware of as to why he lives at home.   I lived at home as an adult for years and people liked to talk **** about me too but the truth is I was the one paying for everything.  My dad got sick and couldn't work anymore, my mom had to quit working to take care of him.  My dad still got disability and a decent amount for having to medically retire at 48 but their expenses got higher due to medical expenses.  I had a full-time job making decent money and was going to school, then I added a second part-time job.  I still had and could do nice things which seemed to bother people.  I never corrected anyone because it was none of their business and in the end they still would have believed what they wanted to.  I worked so much 2 years after my dad died..  I paid their house off.

Your cousin doesn't owe you or anyone else any explanation of why he does what he does.

Stay in your own lane.

Honestly I would resist the urge to call him out.  Anyone that matters probably already knows he is a full on poser.

Calling him out could well backfire on you and you may just end up looking bad or certainly risk being labeled "the bad guy."  Recommend letting him go.  More than likely if you do, it will fall on deaf ears and he will just label you as "being jealous of him."  (posers use that to justify, deflect and rationalize their behavior).

Just ignore and when that becomes difficult, grit your teeth and bite your tongue.  Limit your time around this cousin as much as possible so you don't fill your mouth with blood.   Just give him the space and rope - sooner or later he will "hang himself" on his lies.

Good luck - I know it will not be easy.

He is not making the rest of his family look bad. He is a grown man and only makes himself look bad.

Why is this any of your business?  Who  the heck cares if he brags or even lies about his Vegas trips.