The preposition at is used with the word bad or good to indicate proficiency or skill in a particular activity. Therefore, bad at tennis is the standard usage.

১. Bad in is often used for subjects (like in history) but not for sports.
২. Bad about is used to express feeling sorry or guilty about a situation.
৩. Bad with is used when describing how someone handles objects or people.

অতিরিক্ত তথ্য: Common collocations like good at and bad at are vital for natural English.