"Out of My System" is pop vocalist Feargal Sharkey's last single of 1988 (not including promo single "If This is Love") and second single from his second album Wish.
 A promotional video was filmed for the song, and Sharkey performed the song on the Dutch show TopPop.
Seán Feargal Sharkey (born 13 August 1958) is a singer from Northern Ireland most widely known as the lead vocalist of pop punk band The Undertones in the 1970s and 1980s, and also for solo works in the 1980s and 1990s.
 His 1985 solo single "A Good Heart" was an international success.
 After becoming less musically active in the early 1990s, he has performed various roles supporting the UK's commercial music industry, winning several awards and honours for his work in that area.
Feargal Sharkey is the first solo album of former Undertones singer Feargal Sharkey.
 The album was released in 1985, peaking at #12 in the UK and contains Sharkey's best known single "A Good Heart" his only No. 1.
Constantine is the solo debut album of rock singer Constantine Maroulis.
 It debuted at number 75 on the Billboard 200, selling around 9,000 copies in its first week.
"Listen to Your Father" is pop vocalist Feargal Sharkey's first single as a solo artist, released in 1984.
 The single's two tracks did not feature on Sharkey's self-titled 1985 debut album "Feargal Sharkey".
"Someone to Somebody" is pop vocalist Feargal Sharkey's first single of 1986 and last single of the year to be released in the UK.
 The b-side for the single "Coldwater" was exclusive to the single, an instrumental written by Sharkey himself.
 The song was taken from Sharkey's self-titled solo debut album "Feargal Sharkey".
 A promotional video was created for the single which featured Sharkey performing the song in a restaurant.
Athanasios Demetrios Maroulis (born September 22, 1964) is an actor, vocalist and record producer born in Brooklyn, New York.
 He is the older brother of singer Constantine Maroulis and also has a sister, Anastasia.
Constantine James Maroulis ( ; born September 17, 1975) is a Greek-American actor and rock singer from Wyckoff, New Jersey.
 He was the sixth-place finalist on the fourth season of the reality television series "American Idol", and received a nomination for the Tony Award for Best Performance by a Leading Actor in a Musical for his role in "Rock of Ages".
 He starred in the title role in "Jekyll and Hyde" on Broadway, for which he received a Drama League Award Nomination for a Distinguished Performance Award.
"Loving You" is pop vocalist Feargal Sharkey's second single as a solo artist, released in 1985.
 The single's two tracks did not feature on Sharkey's self-titled 1985 debut album "Feargal Sharkey".
Pray for the Soul of Betty (often known by the acronym, "PFTSOB") was a hard rock band from New York City.
 The band consisted of Michael Hamboussi (drums), João Joya (guitar), Taylor, C.R. (bass) and lead vocalist Constantine Maroulis.
 On March 20, 2006, Maroulis announced his departure on the band's official message board, and on May 13, 2006, drummer Hamboussi posted in his MySpace blog that PFTSOB had officially disbanded.

Question: What do Constantine Maroulis and Feargal Sharkey have in common? 
Answer: singer