American muscle is the collective term for high-powered American cars, particularly those from the 1960–70s. Related words: high-performance engines Mach 1 muscle car V8
Swalla is a dialectical or slang pronunciation of swallow, prominently appearing in hip-hop lyrics with respect to drinking alcohol or performing oral sex on men.
In letters and text messages, xxxx symbolizes a series of kisses, used as an affectionate sign-off or goodbye. It's sometimes used to censor vulgar words or as filler text for unknown characters.
ISTG is an acronym that means I swear to God. It can be used to convey extreme seriousness, exasperation, or surprise, and is usually used outside of a serious religious context.
GFG is an acronym that means good fucking game, and it is used sarcastically in online gaming. A more sincere version is GG, or good game. GFG is also used to mean gift from God.