I flew on easyjet this week. Couldn't do the seatbelt up - there was a good 2" gap between the ends and I had to ask for the extension belt.
I have flown BA, KLM and other long haul airlines in the recent past and not one has been this bad. I have always fitted in, even if snugly. The cabin crew who fetched me the belt, and the very slim lady next to me were both very kind/discreet about it.
I had (honestly) been planning to use the return flight to draw up an updated workout plan anyway, but I am almost too embarrassed to open the relevant document as it clearly shows exercise and then there'll be me with the fattybelt over her gut.
Shame on me 
(Have NCd for this, feel awful
. Was gonna post in 30 days only but am hoping that people here might be a smidge more empathetic about this - I dont need even more of a kicking than I am already giving myself)