They're claiming double standards.
On Christmas Eve, LFC favourite Roberto Firmino was pulled over by Merseyside Police in Liverpool city centre, and subsequently charged with drink-driving.
The Brazilian international is due to appear in court the day after Liverpool's January encounter with title-rivals Chelsea.
A police spokesman said: "Merseyside Police has charged a 25-year-old man with drink driving after his car was stopped in Liverpool city centre in the early hours of Saturday, 24 December 2016.
"Roberto Firmino, from Liverpool, will appear at Liverpool City Magistrates' Court on 31 January."
Regardless of club allegiance, everyone can agree that drink-driving is highly irresponsible, and anyone found guilty of the offence deserved nothing but condemnation for their behaviour.
However, Manchester United fans are particularly annoyed with the press coverage of Firmino's charge, when compared to the negative attention Wayne Rooney received for drinking whilst on international duty some weeks ago.
The Mirror's back page in particular is the focus of much of the chagrin. The headline - following Liverpool's 4-1 victory over Stoke City - reads: 'THE DRINKS ARE ON ME'.
As well as this, the story contains phrases such as 'Firmino shrugs off drink-drive rap' and 'Roberto Firmino bounced back from his drink-drive charge'...

United fans are using the report as evidence that the media are hypocritical in their treatment of Jose Mourinho's side, and that there is a level of bias in the coverage of both Firmino and Rooney stories.
https://twitter.com/Sean_R_D/status/814458849893687296
https://twitter.com/PaddyG96/status/814257002780233728
https://twitter.com/NyiraLydieMUFC/status/814457804924866561
https://twitter.com/ManUtd_HQ/status/813766112240340992
https://twitter.com/FullTimeDEVILS/status/814247222393110528
https://twitter.com/Doc_Joshi/status/814248669948026880
https://twitter.com/MUFC_HP/status/814248203793166336
https://twitter.com/andrewyee/status/814434426285420545
https://twitter.com/DrunkVoltron/status/814433485117132800