bb cas is a Tony Hawk Create-A-Skater with modded balance, after the infamous "13 stat" was removed from online use on THPS4 people started to use the bb cas on THUG (and games onward) to set illegitimate high scores this is notorious with players like Luke.MC & ixiL.
bb cas could also mean you do shit so effortlessly it looks like you're cheating.
Guy: Do a Manny Test No Way YO ass 10 Billed ELA on THAW!
BB Cas User: *197 Regular Stance Manual*
Guy: Nigga Yo Bitch ASS CHEATING LMFAO!
EX 2:
Guy 1: I been balancing these hoes like I got a bb cas
Guy 2: Na, Word how you be doing that?