I'll go with the (standard?) BBJ definition of a bad beat: something beat your quad 8s or better. Then I will buy you a beer or three to cry into (except for lilg, who gets warm milk).

A shortstack jams AIPF with AJ, gets called by a deepstack with A5, flops a 5. This is not a bad beat, and does not entitle you to verbally abuse the deepstack for 2 minutes until your chat is turned off. To paraphrase Rick Paterno, act like you've been at a final table before.