The wimp should have picked out the behaviour of the bullies and told them they shouldn't be acting in this way, and he should not have wanted any approval from them whatsoever.
It is really quite tough when he's only 18 and they're 30. Because he might think that there's some truth to what they're saying, being younger.
It sounds like he was just in an awkward situation entirely..
Since you've witnessed this, I think you tell the wimp that he shouldn't hang around with them and take this abuse, just avoid them entirely, and also tell the bullies they shouldn't pick on meek & harmless people