Reggie, to Archie, in Archie Comics

• Ally who's not completely an ally
• Supporter to keep a watchful eye on
• Fake chum
• Semi-opponent
• Portmanteau for a false ally
• Good bud who may be regarded with some suspicion
• Faux ally
• Buddy to be wary of

Wiktionary Word definitions in Wiktionary
n. 1 (context humorous English) Someone who pretends to be your friend, but is really your enemy. 2 (context humorous English) A fair-weather friend who is also a rival.