Just when you figured that the gentlemen callers had stopped sipping mint juleps on the bachelorette porch of Sirius XM Radio (NASDAQ:SIRI), out comes the poison.

The satellite radio giant is adopting a poison pill clause in an 8-K filing this week. It essentially thwarts hostile takeovers, by granting existing shareholders diluting rights if a potential acquirer snaps up more than 4.9% of the company's stock. Liberty Media (NASDAQ:LCAPA) -- with its 40% stake in the company -- is naturally exempt from the provision.

I'm no fan of poison pills. You shouldn't be, either. They're typically called "shareholder rights plans" but they may as well be called "shareholders wronged." Instead of letting a higher-bidding outsider offer investors an exit strategy at a premium, it forces the prospective suitor to come to terms that are agreeable with the existing board. It's like picking up a date, only to find a chaperone -- and a chastity belt -- attached to the outing .

Sirius XM is an attractive buyout candidate. Despite a history of red ink, Sirius XM had no problem attracting capital when it needed an influx of funds. Liberty Media and EchoStar (NASDAQ:SATS) stepped up with competing bids to bail out the satellite radio provider in February.

Liberty Media and EchoStar's Charles Ergen have interests in satellite television -- DirecTV (NYSE:DTV) and DISH Network (NASDAQ:DISH), respectively -- so they already appreciate the coast-to-coast appeal of satellite-beamed subscription services. Sirius XM may be losing money, but it's hard to refuse a monopoly with more than 19 million monthly subscribers.

Sirius XM is also an attractive buyout candidate to any profitable company with no love for the IRS. Sirius XM has rung up billions in cumulative losses over the years, which can be carried forward to offset the tax bite on billions in eventual profits. The transferability of that perk is a delicate and contested issue, and it's just one more reason why a potential buyer would want to play nice with Sirius XM, instead of storming in unannounced.   

This doesn't mean I'm warming up to Sirius XM's Rights Plan. However, I will have to concede that some poison pills aren't entirely tough to swallow. CBS (NYSE:CBS) came to terms with CNET Networks last year, shortly after it rolled out a poison pill. An even happier ending was in store for auto-parts retailer CSK Auto. It adopted a poison pill defense after larger rival O'Reilly Automotive (NASDAQ:ORLY) made an unsolicited offer to take it out at $8 a share. O'Reilly made nice a few weeks later, with a deal valued at $12 a share.

If a buyer really wants a company, it won't let a poison pill get in the way. However, we may never know whether the extra hassle forces shareholders to settle for less. It certainly has a way of clearing up the front porch, leaving abandoned mint juleps in its wake.

More news than static on Sirius XM:

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Longtime Fool contributor Rick Munarriz subscribes to both XM and Sirius. He does not own shares in any of the companies in this story. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.