I hope Adrian's actually doing some work at college - he seems to spend all his time socializing!

socializing 是动词 socialize 的现在分词形式。socialize 由词根 social（社会的、社交的）加上动词后缀 -ize 构成，意思是"进行社交活动、与人交往"。在句中表示"把时间花在社交活动上"的行为。