The most encouraging thing about the eighth-season start for “Entourage” (HBO, 10:30 p.m.) is that it is the last season.

After a longstanding slump, having an end in sight might just be the thing to slap it back into shape.

As it begins, Adrien Grenier’s Vinnie Chase, the star around whom all the others orbit, is just exiting rehab, with a renewed disposition toward sobriety and a bad idea for a movie that nobody can talk him out of.

His buddies are walking on pins and needles trying not to say the wrong thing and trying to extricate any possible drugs from the house.

The show has long since been undermined by the fact that the childhood buddies wouldn’t most likely still be fully intact and living together eight years later in Hollywood. But now the group has gotten bigger, with Scott Caan and Andrew Dice Clay, of all people, part of the gang.

Dice is in what looks to be a singularly unfunny adult cartoon series about foul-mouthed monkeys with Kevin Dillon’s Drama, the only consistently funny character. The other two – Kevin Connolly’s E and Jerry Ferrara’s Turtle seem to be stuck in permanent ennui due to their respective relationships; worse than both is Jeremy Piven’s Ari Gold, trying to adjust to separation from his wife.

There are still occasional smart references to prevailing personalities (Bobby Flay is announced to be a sworn enemy; someone holds up a sign that says “Winning!” in reference to a Hollywood story more interesting than anything on the series. But the narrative regularly trips up on the relationship issues and there’s a kind of desperation in the show-ending cliffhanger moments that make you think the makers have lost their touch.

It all seems inferior especially since it comes alongside the best comedy on TV, now working at full force, “Curb Your Enthusiasm” (HBO, 10 p.m.).. Tonight’s episode is a highlight as well – a parable of Middle East problems as depicted in the choices of restaurants in Los Angeles. The show’s creator and star Larry David also shows off a new role among his friends: the social assassin, who is able to tell what he thinks when everyone else is afraid.