What cultural faux pas should I try to avoid making in Keflavik?

"In Keflavik, it's considered rude to show up unannounced at someone's home. Always make sure to call ahead and arrange a visit. Avoid comparing Iceland to other Scandinavian countries. Icelanders are proud of their unique culture and heritage and may not appreciate the comparison. Do not litter or disrespect the environment. Icelanders are very environmentally conscious and take great pride in their country's natural beauty. Avoid discussing whaling. It's a controversial topic in Iceland and can lead to heated debates. Do not expect everything to run on a strict schedule. Icelanders have a more relaxed attitude towards time, which can be frustrating for visitors used to punctuality. Avoid being overly loud or boisterous in public places. Icelanders tend to be reserved and value their personal space. Do not assume everyone speaks English. While many Icelanders are fluent in English, it's polite to learn a few basic phrases in Icelandic. Avoid making jokes about elves or trolls. Many Icelanders take their folklore seriously and may not appreciate the humor. Do not overtip. Tipping is not customary in Iceland as service charges are usually included in the bill. Avoid walking on moss-covered lava fields. The moss is delicate and can take decades to regrow if damaged," remarked another expat in Keflavik, Iceland.