Do you think I should ask to use my wife's toothbrush?
Why do you want to use her toothbrush?
It gives me pleasure of licking her germs.
I understand that you get pleasure out of using your wife's toothbrush, but you need to leave her toothbrush alone. Sharing a toothbrush is not healthy behavior and your wife will be disgusted if she finds out that you do it.
How? I think she will like that I'm being honest.
Even if your wife appreciates your honesty, it's still unhealthy for you to use her toothbrush. You might regret using it if you end up getting sick.