tip drill n. an unattractive person, male or female, esp. one who is used for sex or money. Etymological Note: There are two supposed etymologies circulating. Neither can be verified. One says tip drill refers to a practice routine by the same name in basketball or football, in which the ball is quickly passed, bounced, or rebounded from player to player. The other says it refers to the power tool of the same name, which has a twisted head but a smooth shaft or body. The latter may be influenced by tool, a derogatory name for someone who is dense, easily taken advantage of, or otherwise operating at a sub-par capacity. (source: Double-Tongued Dictionary)
Further reading
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I cannot substantiate this, but I thought the term originated in basketball.
It’s a warm-up exercise (“drill”). Players form a line, and take turns running up and touching (“tip”) the backboard.
Hence, a “tip drill” is when many people take turns having intercourse with one person.
It can also be used to describe the person who is being shared.