Explanation
In Germany, beckoning someone with your index finger is seen as condescending and disrespectful, akin to calling a dog. It is generally reserved for summoning animals or children, not adults in social or professional settings.
Local Tip
To call someone over politely, use an open hand with palm facing down and wave all fingers together, or simply approach them directly.
How it compares elsewhere
Beckoning with the index finger is considered very rude; instead, use an open hand with palm down and a gentle waving motion.
Beckoning with a finger is highly offensive and can be seen as a challenge; use a hand gesture with palm down and fingers moving together.
While common among friends, it can be perceived as rude or dismissive in formal contexts; a verbal invitation is safer.