Just because you see it on the field during a baseball game or do it around your buddies, doesn’t mean a woman wants to see you scratch your balls. To her, your actions are rude and disrespectful.
If you can’t discreetly scratch (like behind a newspaper or under the table) then excuse yourself for a moment, find a corner and scratch like a dog if it feels good…then return to her.
You’ll get major brownie points for your consideration.
On a side note: If the need to scratch is persistent and it’s not because you liked her enough to shave your “happy zone”, change your brand of detergent or try boxers instead of briefs and let them hang. Still doesn’t reduce or eliminate the problem, see your physician.