A verb used instead of any other offending verb when insulting someone for something they didn't even do, or that you have no proof of.
Is conjugated as such:
I - fat/am fatting
you - fat/are fatting
he/she - fat/is fatting
they - fat/are fatting
1. Omigod, stop fatting everywhere!
2. Fatting?
1. You know, the verb "to Fat"