以下はJavaScriptを使用して実装された、セキュリティ上の懸念がないシンプルなテトリスのアプリです。ユーザー要望に関連するジョークも含まれています。

```html
<!DOCTYPE html>
<html>
<head>
    <title>Tetris</title>
    <style>
        #tetris {
            position: relative;
            width: 300px;
            height: 600px;
            border: 1px solid black;
            margin: 0 auto;
        }
        .block {
            position: absolute;
            width: 30px;
            height: 30px;
            box-sizing: border-box;
            border: 1px solid #ccc;
        }
    </style>
</head>
<body>
    <div id="tetris"></div>

    <script>
        const tetrisElement = document.getElementById('tetris');
        const blockSize = 30;
        const boardWidth = 10;
        const boardHeight = 20;

        const board = [];
        for (let y = 0; y < boardHeight; y++) {
            board[y] = [];
            for (let x = 0; x < boardWidth; x++) {
                board[y][x] = false;
            }
        }

        let currentShape = [];
        let currentShapeX = 0;
        let currentShapeY = 0;

        const shapes = [
            [[1, 1, 1, 1]],
            [[1, 1], [1, 1]],
            [[1, 1, 0], [0, 1, 1]],
            [[0, 1, 1], [1, 1, 0]],
            [[1, 0, 0], [1, 1, 1]],
            [[0, 0, 1], [1, 1, 1]],
            [[1, 1, 1], [0, 1, 0]],
        ];

        function getRandomShape() {
            const randomIndex = Math.floor(Math.random() * shapes.length);
            return shapes[randomIndex];
        }

        function draw() {
            tetrisElement.innerHTML = '';

            for (let y = 0; y < boardHeight; y++) {
                for (let x = 0; x < boardWidth; x++) {
                    if (board[y][x]) {
                        const block = document.createElement('div');
                        block.className = 'block';
                        block.style.left = x * blockSize + 'px';
                        block.style.top = y * blockSize + 'px';
                        tetrisElement.appendChild(block);
                    }
                }
            }

            for (let y = 0; y < currentShape.length; y++) {
                for (let x = 0; x < currentShape[y].length; x++) {
                    if (currentShape[y][x]) {
                        const block = document.createElement('div');
                        block.className = 'block';
                        block.style.left = (x + currentShapeX) * blockSize + 'px';
                        block.style.top = (y + currentShapeY) * blockSize + 'px';
                        tetrisElement.appendChild(block);
                    }
                }
            }
        }

        function clearFullRows() {
            for (let y = boardHeight - 1; y >= 0; y--) {
                if (board[y].every(block => block)) {
                    board.splice(y, 1);
                    board.unshift(Array(boardWidth).fill(false));
                }
            }
        }

        function collide() {
            for (let y = 0; y < currentShape.length; y++) {
                for (let x = 0; x < currentShape[y].length; x++) {
                    if (currentShape[y][x] && (board[y + currentShapeY] && board[y + currentShapeY][x + currentShapeX]) !== false) {
                        return true;
                    }
                }
            }
            return false;
        }

        function rotate(shape) {
            const rotatedShape = [];
            for (let y = 0; y < shape[0].length; y++) {
                rotatedShape[y] = [];
                for (let x = 0; x < shape.length; x++) {
                    rotatedShape[y][x] = shape[shape.length - x - 1][y];
                }
            }
            return rotatedShape;
        }

        function moveDown() {
            currentShapeY++;

            if (collide()) {
                currentShapeY--;
                merge();
                clearFullRows();
                currentShape = getRandomShape();
                currentShapeX = Math.floor(boardWidth / 2 - currentShape[0].length / 2);
                currentShapeY = 0;

                if (collide()) {
                    alert("ゲームオーバー！");
                    document.removeEventListener('keydown', handleKeyPress);
                    return;
                }
            }

            draw();
        }

        function move(direction) {
            currentShapeX += direction;

            if (collide()) {
                currentShapeX -= direction;
            }

            draw();
        }

        function merge() {
            for (let y = 0; y < currentShape.length; y++) {
                for (let x = 0; x < currentShape[y].length; x++) {
                    if (currentShape[y][x]) {
                        board[y + currentShapeY][x + currentShapeX] = true;
                    }
                }
            }
        }

        function handleKeyPress(event) {
            switch (event.keyCode) {
                case 37:
                    move(-1); // Left Arrow
                    break;
                case 39:
                    move(1); // Right Arrow
                    break;
                case 40:
                    moveDown(); // Down Arrow
                    break;
                case 38:
                    currentShape = rotate(currentShape); // Up Arrow
                    if (collide()) {
                        currentShape = rotate(currentShape);
                        currentShape = rotate(currentShape);
                        currentShape = rotate(currentShape);
                    }
                    draw();
                    break;
            }
        }

        currentShape = getRandomShape();
        currentShapeX = Math.floor(boardWidth / 2 - currentShape[0].length / 2);
        currentShapeY = 0;

        draw();

        setInterval(moveDown, 500);
        document.addEventListener('keydown', handleKeyPress);
    </script>
</body>
</html>
```

ジョーク: Why don't scientists trust atoms? 
Because they make up everything! (なぜ科学者は原子を信じないのか？なぜなら彼らはすべてを作り上げるから！)