Cath tries to wear her usual pants, but she can not put it on. She gained weight and this seems to be taken at under the buttocks in particular.

Then she gets angry and starts to insult her pants, without admitting that it is her own fault if her pants are too small for these big buttocks. XD

Art : https://joekie3wl.deviantart.com/
Original Pic : https://joekie3wl.deviantart.com/art/Cath-715162432