Coined shortly after the 2010 general election in the UK Yellow Flu takes its name from the party colours of the Liberal Democrats.
Yellow Flu typically manifests itself within local party activists and councillors who do not get to directly enjoy the fruits of being in government. Namely a ministerial car or occasional dinner with News International lobbyists. First symptoms include a growing reluctance to defend Liberal Democrat supported policies beyond blaming the Labour party, the weather, or coalition, medium level symptoms include erratic opinion shifts and outbursts of crying. Terminal Yellow Flu results in resignation and oft repeated vows to never give Nick Clegg the time of day again.
Yellow Flu has given rise to another illness specific to Liberal Democrats. With the Conservative party considering the Liberal Democrats barely worth bothering with beyond a whip sheet, the Labour party is at its warmest, now completely opposed to talking to the Liberal Democrats with words other than "sellout", "lackies" or "shower of useless Tory supporting shites". This secondary illness is known as Yellow loneliness and it's becoming increasingly common for this to strike quickly after the onset of Yellow Flu.
Voter2: "What? Why? I thought he was chuffed at having made the Tories implement the pupil premium, even though it was in both their manifestos?"
Voter1: "No. Apparently he can't support the coalition now"
Voter2: "After he's sold off our NHS, put us back in recession and propped up the Tories for two years?"
Voter1: "Yup. Must be Yellow Flu."
Voter3: "Sorry I was just passing, did you just call a Liberal Democrat a twat? I quite agree. I remember tuition fees even if they don't"