リグマ is pronounced "riguma". Japanese らりるれろ/ラリルレロ (ra ri ru re ro) sounds do not have a direct equivalent in English, but English R and L sounds are the closest, and we tend to defaut to r for any Japanese words or romanization (aka writing Japanese words with the Latin alphabet, which is referred to as romaji). But their "R"s can also be interpreted as L for loan words or words from another language depending on the word. Riguma would be spelled the same as ligma would in romaji, and when spoken would be pronounced the same. Ligma is a joke disease people claim to have so that when someone asks them what it is they can reply with "ligma balls", which sounds like "lick my balls." リグマボールス would be romanized as "riguma bōruzu". Bōruzu is how they'd write the English word for balls, so "riguma bōruzu" sounds like "Ligma balls" and is how you would say/write it in katakana.