In which year did the user who has given the most number of "short" tips join the Yelp?
year the user join the Yelp refers to user_yelping_since_year; most number of short tips refers to MAX(COUNT(tip_length = 'Short'));
SELECT T2.user_yelping_since_year FROM Tips AS T1 INNER JOIN Users AS T2 ON T1.user_id = T2.user_id WHERE T1.tip_length LIKE 'short' GROUP BY T2.user_yelping_since_year ORDER BY COUNT(T1.tip_length) DESC LIMIT 1