To turn of strict mode in MySQL you’ll have to locate your MySQL instance’s .ini file and look for a line like:
sql-mode=STRICT_TRANS_TABLES,…
And remove “STRICT_TRANS_TABLES” and restart the instance.
Unfortunately the scope of this setting is for the entire MySQL server instance and can’t be done on a schema-by-schema basis…
I’d only do this as a workaround, though. My guess is that BuddyPress should be supporting strict mode, and there’s just a bug in there…