Gonococcal Urethritis: This is the most likely diagnosis given the symptoms of dysuria and pain at the meatus, especially with a history of unprotected insertive anal and vaginal intercourse. Neisseria gonorrhoeae is a common cause of sexually transmitted infections (STIs) that can lead to urethritis, characterized by dysuria and meatal discomfort.

Chlamydial Urethritis: Similar to gonococcal urethritis, Chlamydia trachomatis can cause urethritis, leading to symptoms of dysuria and meatal pain. It is another common STI that can result from unprotected sexual intercourse.
Herpes Simplex Virus (HSV) Infection: HSV can cause genital herpes, which may present with dysuria, especially if there are vesicles or ulcers near the urethral meatus. The pain can be severe and is often accompanied by other symptoms like itching or burning.
Trichomoniasis: Caused by Trichomonas vaginalis, this infection can lead to urethritis and symptoms of dysuria, though it is more commonly associated with vaginitis in women.

Syphilis: Although less common, syphilis (caused by Treponema pallidum) can present in its primary stage with a chancre, which may cause pain and dysuria if it is located near the urethral meatus. Missing this diagnosis can have significant consequences due to the potential for progression to secondary and tertiary syphilis.
Human Immunodeficiency Virus (HIV) Infection: HIV can increase the susceptibility to other STIs and may present with symptoms similar to those of other infections listed here. Early diagnosis of HIV is crucial for the management and prevention of complications.

Lymphogranuloma Venereum (LGV): Caused by certain serovars of Chlamydia trachomatis, LGV can lead to urethritis and systemic symptoms but is less common in many parts of the world.
Mycoplasma genitalium Infection: This bacterium can cause urethritis and is recognized as an emerging cause of STIs. However, it is less commonly diagnosed due to the lack of routine testing in many clinical settings.