You can find some lists which state bougainvillea will not be browsed by deer, and others that say it will. What this discrepancy demonstrates is that there is no such thing as a 100% deer-proof plant. Different deer have different taste preferences. Also, when hungry enough, deer will eat almost anything. All one can really say is whether a deer either prefers, demonstrates less preference, or avoids a particular type of plant. The link below has a list of plants organized on this type of model.