Just curious about this . . . say a guy enlists, does his regular stint of service, gets an honorable discharge, goes home, re-establishes his civilian & family life . . . and then gets recalled.
What happens if he fails a drug test, gets an "objectionable" tattoo, or something else of the sort?
The key to your question is the word "discharge". Once you are discharged as an enlisted man that ends your obligation. It would take an act of congress to bring you back into military service against your will.
Separation though is an entirely different deal. For enlisted personell until you serve your eight you are not discharged but separated. Meaning you still have some time left on that 8 years. (keep in mind though that if you are on active duty that stop loss can retain you past your 8 year obligation)
Retirement? Now that's an entirely different deal. For those enlisted types and non-flag officers that think they're retiring at 20 - well - not really - they're being seperated. They're essentially on retainer until they hit 30 years. I know quite a few Navy Chiefs that got called back in during the late 70's and early 80's who had
retired at 20. At 30 years enlisted personell will receive discharges. There may be exceptions for E-9's. They may be treated the same as Flag Officers though I am not sure about that. I'm not sure what status Officers below the rank of O-7 retain.
Flag Officers are never actually retired/seperated/discharged and can be called back to active duty essentially until the day they die though for practical reasons once they hit mid 60's or so it probably wouldn't happen.
Officers can resign their commissions if they choose which essentially breaks their association with the military and will fall into that category of it takes an act of congress to drag them back. What happens to an Officer's retirement pay if they choose to resign their commission after retiring is anyones guess though I imagine they'd lose it. It would be unusual though for an officer to resign their commission without really good reason after retiring.