Can I pull the fake flowers off of cacti at the store?
Why would you damage property that doesn't belong to you?
Because they are visually unpleasant to the eyes.
Beauty is subjective and what you may find unpleasant isn't necessarily what someone else finds unpleasant. Instead of damaging something at the store that you haven't paid for, you shuold just remove yourself from the situation if it bothers you that much.
It doesn't bother me that much but I'm going to do it anyways.
The shop employees will catch you and you'll be forced to pay for the damages. The cacti isn't going to bother you if you simply walk past or ignore it. Try finding another store to shop at if you're that tempted.