I was just reading this on an online max-DPR build and there were some who thought using the metamagic twinned spell on the warlock cantrip was illegal, and some who thought the opposite.

Twinned Spell, PHB page 102 (emphasis mine)

When you cast a spell that targets only one creature and doesn't have a range of self, you can spend a number of sorcery points equal to the spell's level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip).

So can the sorcerer's Twinned Spell metamagic class feature be used with Eldritch Blast?