1) Getting the words gefeliciteerd and gecondoleerd mixed up. One means congratulations. The other means condolences. You can get away with the mistake at a birthday party but not at a funeral.
2) Accidentally buying vla instead of milk and only discovering the mistake when you are serving tea to guests (and the resulting splosh lands in their laps).
3) Returning to your home country and confusing the shop workers there by unintentionally speaking Dutch to them.
4) The moment you accidentally use a Dutch word in an English sentence without realising. Even worse; the Dutch word just happens to sound like an English word, resulting in a completely nonsensical sentence.
5) Spending ten minutes searching amongst the bicycle racks for your bike, convincing yourself it has been stolen when you can’t find it, informing the police and then suddenly remembering you left it at home today.
6) Spending ten minutes trying to unlock your bike, cursing the useless thing, kicking it then suddenly realising it’s the wrong bike.
7) Angrily telling a Dutch person that they have to speak Dutch to you (not English) so you can learn their language. Then, when they finally comply, you realise you cannot understand a word they are saying.
8) Spending ten minutes nodding and smiling along to a Dutch conversation you do not understand. Then suddenly realising that they just asked you a question (and think you have understood everything they have said so far).
9) The awkward hesitation of saying goodbye to a female acquaintance when you are unsure if you are at the cheek kissing or handshaking phase of familiarity. Cheek kisses might be too forward but a handshake might be seen as unfriendly.
9b) Both being within a group of people you do know well (and usually give cheek kisses too) when the above situation happens.
10) Suddenly realising that you have been over familiar with everyone by using the word ‘je’ instead of ‘u’ when refer to them in conversation.