As an ex BA gorgeous trolley dolly I can say cabin crew do use the "cold" or "blocked ears" excuse when it suits them. I have vivid memories of crew having more than a cold on certain routes, but flying because the trip was high in allowances. I also remember crew comparing rosters on the crew bus to the a/c etc where it was common for some to say, " I won't be doing that horrible trip darling...I'm due a sick period around then!"
I worked for BA when crew had it extremely easy...and I was equally guilty of frequently going sick because I didn't want that vile MIA or because I wanted the 17th off didn't get it, but still went ahead with plans. Another reason for sickness was to change your roster - if you report sick, you get your trips wiped and from experience they are replaced with some nicer ones when you call in fit. Not sure how things work now, but I bet things haven't changed much.
Like someone said on here, crew throw their toys out of the pram far too often....and I used to spit my dummy out all the time until I grew up and left.
Now, where did I put my lemsip?