1 Samuel 2:15 & 16

"But even before the fat was burned, the priest's servant would come and say to the person who was sacrificing, 'Give the priest some meat to roast; he won't accept boiled meat from you, but only raw.' If the person said to him, 'Let the fat be burned first, and then take whatever you want,' the servant would answer, 'No, hand it over now; if you don't, I'll take it by force.'" NIV translation

Eli's sons were even more corrupt than the rest of the priesthood as they did not even wait for the meat to be boiled. They were wanting to roast it instead of having boiled meat. The boiling was to remove the fat and the blood which was set aside for God so, by insisting on taking the raw meat, they were taking God's portion. We also see that they had servants to do the dirty work for them and they would even threaten the people if they would not give in to them. The priesthood had become a bunch of lawless thugs preying on the people.